lots of good posts on here that will walk you through it.
My advice, go through Silencer Shop. They will basically do all the paperwork for you, but you will see how the process works.
It seems those that file as an Individual are seeing faster approvals than those who are using a Trust. Already having a stamp go through has no effect on the timeline of your 2nd or 3rd stamp as far as everything I read.
What really determines how long your wait is... from my research, how many are in front of you and what rate they are processing them.
There are plenty of good Class III dealers right here in Indiana. I like to keep the business local. Any of them can help you get the paperwork right, and help you understand how it all works.
It's not as difficult as it seems at first. Personally I still think a trust is the best legal vehicle long term and it's worth the extra wait time IMO.
Form 3's (dealer to dealer transfers) have really sped up so because of that I'd purchase the suppressor online just to avoid state sales tax.