Don't forget that Festool will increase their prices again on April 1. In the "dealer" section, someone posted the list of prices after April 1. Dust extractors will see a significant price increase, as much as 6-7%. I think you need to do the math and figure out what works better for you financially (with the coming price increase in mind) and what your further plans are. You can buy MFT/3 in a package only with the track saw. This is your only opportunity to save on MFT/3. You can buy a dust extractor in a package with many other tools. You will most likely buy more than just the track saw, so there will be many opportunities to buy the dust extractor. If you can, order both (maybe TS55+MFT-3 and Midi + sander).
You need a dust extractor to use with TS55. Otherwise, you will be all covered in saw dust. Festool tools work really poorly without a vacuum, worse than most other tools. You could use a regular shop vacuum with TS-55, but as a minimum you would need to buy a flexible and thin hose. The cheapest option is the 36 mm Bosch hose which is around $40 on Amazon. And it still will be a hassle without autostart.
Regarding which vacuum to buy: I have a Midi, 2xCT26, and CT36AC, and the Midi is my favorite. The only advantages of CT26 is that it can be used with a boom arm (a nice thing to use with MFT/3, but requires a dedicated vacuum) and that you can plug in a "Y" into it (which is a necessity for the router table). CT26 is definitely larger than the MIDI, but its suction is pretty much the same and all features are the same. You do not have to buy it local, you can as well order it online. Most online retailers ship Festool for free. Just make sure to place your order before March 31.
Mini is probably does not make much sense because it is neither much smaller nor any lighter, but its dust bag is quite a big smaller.
Good luck!
MFT/3 is a great table for work, but it is kind of small. It allows you to cut only relatively small pieces, albeit with a high precision. For anything large, you will have to cut elsewhere.