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.