Take the Ender 3 Pro if you want to buy one of the two, this is the slightly improved version of the Ender 3.
and in terms of print resolution. Even though the Pro should be able to do 0.05mm, you will rarely use that and 0.01. I print most of my stuff in 0.2mm. For most things this is enough. Unless you really want to print small but very fine/detailed things. The finer something is the longer it takes to print. And depending on the size of the object, the printing time can be several hours. With larger objects and <0.2 also well >10h.
Yes, it is possible, but only very slowly. If you want to print TPU reasonably fast, I recommend upgrading to a direct drive extruder. I don't think it's on sale at Digitec, but there's a great shop called "Bastelgarage". I think links are forbidden here but googling helps :-)
After some research, it is compatible with Windows, Mac and Linux but no details on the distribution. However, the most important thing is the application you are going to use such as Cura, Tinkercad or Meshmixer.