I thought for 1rm you do standard warmups for your 5rm, then do 1 rep of 5rm weight, then go 1rm.
For belt criteria there's a whole chapter in SS about it. Basically, you want one that's the same width all around. Most belts are tapered so they're wider in the back and the front is thin. This is bad and dumb, since the whole point is to give your abdominal muscles something to push against which will help stabilize you and enable you to use more weight. The first time you squat or dl with a belt, you will definitely notice some ab soreness. You want a belt that's 10-13mm thick, 13 is the maximum you can use in powerlifting competitions. There are leather, suede, and velcro belts. I believe the velcro ones are more specific to olympic weightlifting since they're a tad less heavy and you have more mobility but a little less support. The suede Inzer belt is the standard, it costs about $50 shipped.
You'll use the belt for squatting and deadlifting definitely, and possibly benching and pressing as well. I find it really helps engage your abs during the press. During the bench it can help you maintain your arch, but it's less helpful on the bench than the other lifts. You probably won't want to use it on powercleans.
You'll want to wear it pretty tight, as tight as you can get it while still being able to fit 2 fingers inside of it. You'll see lots of brotards wearing a belt around really loosely for their curls and lat pulldowns, it's a mystery.
As it so happens, the 70sbig.com front page is on belts today. They also had 2 more sections about why to wear a belt and what kind to pick.
www.70sbig.com