If you want an antenna to last a lifetime spend a bit more and buy a DB404. I run these on all my repeaters and have yet to have an issue including when they are iced over or not. I also use one as a portable antenna on my mobile repeater and being all aluminum holds up better than any fiberglass stick i have ever tried.
There is a few controllers that came as options with the 1225. The basic internal controller is the best i have found. I have mine set for ID only and they work fine. There was a Zetron controller that many added to give phone interconnect and other features. Personally unless you need a special feature stick with the basic programming. Using the internal controller is the best. To change to an external controller you need to reprogram it for external control.
I would track down the land owner and talk to him. We have done this for Search and Rescue events and 99% of the time they are fine with it. Most of our stuff is temporary for a few days but never really discussed a permanent site.
I highly recommend you DO NOT use LMR400 for a repeater. Get some hard line. There are lots of info out there on the issues with LMR400 on duplex operations. I have tried it a few times with mixed results.
Spend the money on the mobile duplexer and you should be fine. I have mine tuned to the middle frequency and can go up and down without much degradation. There is some but 99% of the time i am in the middle. The only time i had to go to the bottom of the list was at a NASCAR race and i was only using low power anyway.
Guess it depends on how you set it up. I have a live feed for SAR in my area. The scanner does scan some GMRS channels as we use them...I am guessing a single live feed of a repeater is not gonna happen, but so far mine have been fine.