Willkommen. Check out this post/thread, which says it's possible (haven't tried it personally).
http://festoolownersgroup.com/festool-jigs-tool-enhancements/dewalt-621-router-with-festool-track/msg327528/#msg327528
Be careful asking tool junkies whether you should buy more tools.
Whether you go for Carvex or RO depends on what you want to do. As to the 125 vs. 150 issue, you'll find a lot of diverse opinions. I didn't plan it this way, but I ended up with a very suitable combination by getting the RO90 first, and then the RO150. If you were just to have one sander, then the 125 might be the one, but having access to the capabilities (and amazing balance) of the 150 for large surfaces, and the the 90 for narrow stock and corner work, I have everything covered, and have never once thought I needed something in the 125 size range.
You really do want to get a dust extractor to make full use of the sander, however.
The Carvex is an amazing machine as well, turning the jigsaw into a precision tool. It was the first Festool I purchased, and the reason why I decided to start greenwashing my shop. The only shortcoming is the base for making angle cuts, which leaves the jigsaw contacting half the surface area of the normal bases. Not a big deal if your bevel cuts are straight, but if you're curving them (or you're back scribing a cut off the edge of a board), you might not be as impressed. Carvex also has the worst dust collection of all the Festools, though it's still better than no DC.
