SteveShannon

Not necessarily. The repeater might have 50 watts of RF power and a great antenna on a tower. 

Chessy68,
Randy (@OffRoaderX) has put together a metric buttload of videos about almost entirely GMRS radios. They’re available under the name “Notarubicon”.
Not everyone appreciates his humor, so if they don’t appeal to there are many others. 
 
Welcome to the forum!

You need either a “barrel adapter” with an SMA female on one side and SO-239 on the other, or a jumper cable with a PL-259 on one end and an SMA female on the other. 
 
Eventually you’ll have every combination of adapter 😁!
Here’s a kit that might help get you started: 
https://a.co/d/1Bzh3h4

Don’t worry about what wrxp381 says he has never felt the need to do. He says that sometimes, but his “needs” are irrelevant to your question. It’s nice to know the output of your radio and it’s simply not true that you can’t test SWR with a handheld.
He may have meant that testing the SWR of a handheld’s antenna doesn’t mean much and I would agree with that.

I have heard a few people mention that Youtube has some good videos going over every aspect of using GMRS and pretty much all GMRS radios. 

Rain in antenna connections is a fairly common occurrence if the connections aren’t waterproofed. PL-259/SO-239 connections are not weatherproof. 
Worst case you might need to replace the cable or at least shorten the cable to get rid of damage caused by moisture in the dielectric layer. 
 

at a minimum, all you need to do is put the radio on the correct corresponding repeater channel, go into the menu and find the CTC or DTC menu (depending on if it is a CTCSS tone or a DPL/DTC tone) for TRANSMIT, select the correct tone from the list, and save the change.  I know you said you are not "technically inclined" but I assume you know how to read, so you might have to read the manual for the exact steps.  Only worry the transmit tone for now, the receive tone is optional.
That is all you need to do.

The aluminum foil won't hurt the magnet at all. Don't worry about it.
Sticking something magnetic on the back side of the foil the magnet can be attracted to is a good idea to hold the foil in place. The foil needs to be a rough square at lest 6 inches on a side or a circle about 12 inches in diameter. Put the magnet mount in the center. 

I can verify that. 🫤
https://forums.mygmrs.com/gallery/image/427-adapters-connectorsjpeg/?context=new
 

You need either a “barrel adapter” with an SMA female on one side and SO-239 on the other, or a jumper cable with a PL-259 on one end and an SMA female on the other. 
 
Eventually you’ll have every combination of adapter 😁!
Here’s a kit that might help get you started: 
https://a.co/d/1Bzh3h4

Don’t worry about what wrxp381 says he has never felt the need to do. He says that sometimes, but his “needs” are irrelevant to your question. It’s nice to know the output of your radio and it’s simply not true that you can’t test SWR with a handheld.
He may have meant that testing the SWR of a handheld’s antenna doesn’t mean much and I would agree with that.

No I didn't. That video was 8 months ago, I just didn't remember that particular "not my favorite" radio being featured. I do remember that you had the picture of your favorite Vice President and former California Attorney General on the monitor in the background. In the whatever available future that lies ahead for me, I'll do a better job in remembering such stuff.

Hi Leo,
Welcome to the forum. 
Congratulations on navigating the FCC licensing site. You’re right that it is not easy. 
It can take a few days between the time the FCC issues your license and the time the bulk download is done for this site. It will eventually happen though. 
If some people here seem like jerks you can add them to your “ignore list.” Then you won’t have to see their posts. 
If there are repeaters preprogrammed in your radio they’re probably just there as examples. Or it may just be that they’re the eight established repeater channels that have the offset programmed in but are waiting for you to program the correct CTCSS tone or DCS code on transmit. 
Again, welcome!

Hi Leo,
Welcome to the forum. 
Congratulations on navigating the FCC licensing site. You’re right that it is not easy. 
It can take a few days between the time the FCC issues your license and the time the bulk download is done for this site. It will eventually happen though. 
If some people here seem like jerks you can add them to your “ignore list.” Then you won’t have to see their posts. 
If there are repeaters preprogrammed in your radio they’re probably just there as examples. Or it may just be that they’re the eight established repeater channels that have the offset programmed in but are waiting for you to program the correct CTCSS tone or DCS code on transmit. 
Again, welcome!

I have the inReach service with my Garmin Tread 10 Overlander Off-Road Nav System in my Jeep. Also, my system has the SOS feature in addition to the email and texting features.

Hi Leo,
Welcome to the forum. 
Congratulations on navigating the FCC licensing site. You’re right that it is not easy. 
It can take a few days between the time the FCC issues your license and the time the bulk download is done for this site. It will eventually happen though. 
If some people here seem like jerks you can add them to your “ignore list.” Then you won’t have to see their posts. 
If there are repeaters preprogrammed in your radio they’re probably just there as examples. Or it may just be that they’re the eight established repeater channels that have the offset programmed in but are waiting for you to program the correct CTCSS tone or DCS code on transmit. 
Again, welcome!

Same as above, plus: keep in mind that aluminum is non-ferrous, meaning that is actually repels magnetic fields. Sure it's thin, but there might be a risk of deteriorating the magnet if left on the aluminum long term. Consider a large steel washer below the magnet to "capture" the magnetic fields, then place that combo on the aluminum foil. 

It is my understanding that that Rubicon guy is really not a Rubicon guy and he is really a Nissan guy with a Chinese made Jeep Key Fob.
Real Izarubicon people drive Rubicons with real American Jeep Keep Fobs.
 

That really depends on how you define "Best", and what is most important to you when shopping for an antenna.

(As I’m sure you know) The problem with zip ties like that is a zip tie concentrates too much force in a small area which can crush the foam dielectric, resulting in impedance issues and SWR problems. 
A cable grip is a better choice:
https://www.dxengineering.com/parts/tmv-hg-400t?rrec=true

I would agree with a slight clarification.  Good quality cables are available at Amazon if you know what you are looking for.  A person can buy Times-Microwave or M&P cables there, but you pay considerably more than you pay for the same cables from DX Engineering, Gigaparts, or Ham Radio Outlet.

You really don’t have to buy another antenna. An SWR of 2.5 isn’t really very high and isn’t going to cost you much. Most people don’t understand how little an SWR of 2.5 means. As an example, the SWR in your cell phone may be around 4 or 5. 
Just try your antenna and see if it works for you. 
At an SWR of 2.5 82% of your power goes out of the antenna without being reflected, but that other 18% is reflected back to the transmitter where it’s reflected back to the antenna again. Then 82% of that portion is radiated and 18% of the reflected power is reflected again. That happens over and over until all the power goes out the antenna or is absorbed as loss by the coax cable. 
 

The bump in wattage will make no difference whatsoever. 
Quadrupling your power to 150 watts would only make a single point of difference on the S-meter.

as @Sshannon, 2.5 is just fine.. Stop overthinking it and enjoy your repeater.

(As I’m sure you know) The problem with zip ties like that is a zip tie concentrates too much force in a small area which can crush the foam dielectric, resulting in impedance issues and SWR problems. 
A cable grip is a better choice:
https://www.dxengineering.com/parts/tmv-hg-400t?rrec=true

I would agree with a slight clarification.  Good quality cables are available at Amazon if you know what you are looking for.  A person can buy Times-Microwave or M&P cables there, but you pay considerably more than you pay for the same cables from DX Engineering, Gigaparts, or Ham Radio Outlet.