I do this paint work all the time. The DTS400 is the best sander for all general paint prep around the house. Having a Rotex - 150? also is a great extra for larger objects/surfaces.
For general paint work, the pad of the DTS400 is ideal. It's one of my 5 sanders and it's the one I use most. I simply love it. Works great on all kinds of trim around the house and also on doors. I do prefer the ETS125 for doors, the eccentric motion of the ETS125 leaves less scratches on doors, but if I don't have that one with me the DTS400 will do just fine.
Forget about the Rotex 90 yet. I mean, if you don't have a DTS400 yet, get that one first and perhaps later a RO 90. Nothing bad about the RO 90, but I think it's sincerely overrated here on the board, especially by the American members who seem to be struck by this "all new Festools are the best ever" virus, like the wheel all of a sudden is reinvented - but it's not. The RO 90 might have a nice powerful motor for it's size but it remains a SMALL sander with a SMALL pad, and that's a SPECIALTY sander and not one for general work. On bigger surfaces (and big means bigger than it's pad size) the RO 90 falls short quickly.
I also recommend the DTS heavily over the RTS. The DTS is so much nicer to work with because of it's pad size and shape. Much more stable in the hand and the iron shape will allow you to work into corners and along edges with great ease. The RTS is not that good with those things, and many times I found myself actually make an effort to keep it straight up, because it has a tendency to tip over to the sides.
Only thing to add is that the small delta shape of a DX 93 or the RO 90 comes in handy sometimes. But only sometimes. In some cases, the DTS400 won't fit for some weird spot you're trying to reach, like behind pipes or something like that. I'm certainly not the type of person that believes in a "one size fits all appraoch", that's why I have 5 sanders for paint work. So maybe, after you have bought a DTS400 you could think about a RO 90 or a DX 93. In this case the RO 90 would be preferable over the DX 93. It is 1,5 times as expensive but it gives you 3 or perhaps even 5 times the sander that the DX 93 is.
As for abrasives, for general work on paint Brilliant 2 and Granat are the papers of choice. They're practically the same. For all the latex paints used in America, as Tom said, Granat might be a slightly better choice. Get a nice selection of grits from 40 to 320. Most work can be done with 80 and 120. If you need to remove A LOT of flaking paint to get to bare wood, Cristal comes into the picture.
