Wow... great first post.
I'd say your tun is perfect for a mash vessel.
1. As for a false bottom, the amount of space needed under the false bottom is minimal with a bottom drain, I'd go with a half inch to inch.
2. I don't have a Blichmann, but some people on here do, such as JohnQ, Sdixon, Fakr, and maybe others.
3. I'm not able to advise on where would be best to have it made, other than to ask a member called NorthNomad. He has an extensive background in stainless steel sourcing.
4. Many of the guys in the club are all grain brewers, and sitting in will be easy to arrange. Also, you are welcome to come to our Mash Occur at the end of March, where a number of members will be brewing together at a club meeting, send a PM to JohnQ for details.