If you go the "solvent Trap" route, you can in fact purchase it before you get your stamp back... It's a solvent trap, not a suppressor. AS LONG AS YOU DON'T DRILL HOLES IN THE END CAP AND THE BAFFLES BEFORE YOU GET YOUR TAX STAMP BACK, YOU'RE FINE. I capitalized that sentence because it is very important.
I've done 1 form 1 so far. I used a solvent trap kit from form1builder.com. They make a great product, but there communication is absolute garbage. The next one I do will be most likely homemade from scratch.
My form 1 trust took about 35 days, and that was with a paperwork screw up on my end that required me to resubmit it.