@WRQI485 Welcome. Since you already have so much of the equipment, I don't see any reason not to go for it. I'm not a repeater expert but there are many people here who can help. Good luck to you.
Mike, it sometimes takes some time for the database to be propagated to myGMRS.com. Just give it a little time and it will show up and you will be able to register.
@roo_ster Welcome back to GMRS. I haven't been at it for all that long but have use it quite a bit since I started. CB doesn't have nearly as many offerings in HT as GMRS. I've used GMRS in the mountains around Cloudcroft NM and didn't have any problems. Although it is "line-of-sight" it isn't like a laser. My son was constantly out of sight around fingers and over hills and we never lost contact.
The only problem I have had so far was trying to penetrate all the trees and houses in my neighborhood. That's were more power really helps. Bumping up from 4 watts to 7-8 watts made all the difference in the world.
I don't go off-roading either but some of the ranch roads I've been on sure feel like it, especially going up and down the really steep places with loose rocks.
Just about any other antenna is better than the stock antenna. The Nagoya has a good reputation. Abbree are also good and much cheaper but they don't make a 701g yet. The do have a 701 however.
According to Land Cruiser Lifestyle "The Midland MXT400’s repeater channels are wideband by default. You can change the direct channels to wideband as well using Midland’s programming cable and PC software."
@WRQC527 I used to be a technical writer. Let me know if you want some help. The questions by @WRZR764 reveal some good topics to cover. Like the fact that giving your ID every 10 minutes is for amateur radio, every 15 minutes is for GMRS.
@gortex2 For the most part I agree with you but new users are constantly asking questions beyond PTT but don't want HAM. I think a good GMRS Primer would be a good thing to have. TexasGMRS.net has some stuff but I haven't looked at it yet. Maybe it would fit the bill.
@Blaise I don't think CB is dead, at least not amongst truckers. Other than that, I agree with you. It would be nice to have some king of standard for seeking help on GMRS while traveling.
I'll second what @WRZD706 said and add that you may want to start with Tone instead of TSQL. This is a common method when first programming a radio for a repeater. That way you hear everything until you are sure you have everything else set up correctly. Then switch to TSQL to squelch out simplex signals.
See https://chirp.danplanet.com/projects/chirp/wiki/MemoryEditorColumns for more information on this.