Here's my $0.02:
1. Most of the used stuff is in the member halls (Red, White, Blue, and Silver), but you will find some in the dealer halls (Orange, Brown and Purple). Don't count dealers out, as they may have stuff priced to move. All of the halls have test tracks (I think), so make sure any engine is tested before buying, and it is a good idea to get the contact info of the seller when making a big purchase. Make sure to visit the Orange Hall - I know you will find Army stuff there.
2. I use my semi-smart phone for the same purpose, and so far have not been asked to stop or take it outside of the hall. Just make sure that when you go to check it that you are not blocking the aisle (some of the aisles in the member halls are fairly narrow with dealers sitting in chairs in the aisles themselves). Using it as a phone is not permitted, but you may answer a call as long as you ask the caller to hold while you make your way out of the hall.
3. Many vendors will take personal checks (remember to write your TCA membership number in the note area), but you should always ask first to make sure. At the meet, cash is king, though, and there are some ATM's on the fairgrounds.
I would also add that if you see something you really want, and the price is good, grab it. It will rarely be there if you pass it up and then try to find it later. I learned this the hard way (but I was able to find something else to spend the money on pretty easily 
).
And don't forget the Thursdays at Fridays OGR gathering at the TGI Fridays on Kenneth Road on Thursday evening (fun usually starts around 7pm and many of us go there for dinner earlier). And the OGR gathering in the grandstands (at the end closest to the Orange Hall) on Friday at 2pm.
Hope to see you there! 
Andy
