Funny how before the ro90, everyone was touting the vast improvement in efficiency of the 150 sanders vs. the 125. Conversations would basically say that " you'd be amazed at how much more work you can cover with that extra inch diameter, by all means get the 150 sanders if you can afford them..."
And now that the ro90 is out, you all are touting it as the best all purpose sander out there... I've checked it out, but as the only sander I'd want, it wouldn't make much sense to do all my sanding with a 3" pad??!
And for someone sanding drywall, a 3" ro sander would be, let's just say, NOT the best choice.
If you want to sand drywall, find yourself the Porter Cable drywall sander - they're available all day long around here on CL for $125-200. I've had one for 10+ years and it's just the ticket and I can't see how on earth the $2000++ Festool version could be much better in terms of dust collection, as the PC is very good in that regard.
I bought myself the little Festool square pad sander and it complements the PC drywall sander perfectly. No more hand sanding at ALL! I don't think for a hand sander I'd want a ro sander for drywall as you'd have to be extra careful not to gouge as you initially place it on the drywall surface.
If you do any amount of carpentry and built-ins, then by all means buy the TS55 FIRST. That and the vac and you'll get the most use for the money spent.
Want to save some money? Any vac will work. I'm not ever one to suggest the rocket engine cheapo Ridgid shopvacs, but Dewalt makes a new line of variable suction premium vacs and the non-Hepa filtered version is around $200. Or the Fein vac is a little closer to $300. The Dewalt is made in Italy. Don't get me wrong, I love my CT22, but aside from being able to stack my systainers on it, which is great, I liked the Fein Turbo vacs better. Quieter, more durable and a bit cheaper and every bit as well, if not better made.
Careful asking how to spend your money around here, you'll always get friendly advice, but not necessarily very practical advice...
Good luck to you.
JT