brewboard post about o-rings from mcmaster
you'll want to trim the dip tube so that you don't suck sediment. i trimmed mine 5/8" and it leaves behind about 7oz in the bottom; not a huge loss. if you trim the dip tubes, you'll want to do it now, so that you can allow the stainless steel to passivate. this just means that the SS needs to heal so that it won't rust in the future. 3-4 days should do it.
if possible, i'd carb cold. i carbed my first keg warm, at like 30psi, and its cold now at 15 psi, but there's just something off with the carb. as long as you get the pressures right it shouldn't be a problem, but it's just a hassle. just yesterday i force carbed a couple cold kegs in just a few minutes. i hooked them up to 25 psi until the gas stopped, shook like crazy for a couple minutes until the other keg was up to pressure, and then kept trading off gassing and shaking. i did this 3 times on each keg. took about 10mins and they're both nicely carbed a couple hours later.