I've got the TSI 170 and I've had a 140 before. Both have been amazing, no problems as of yet (slightly lumpy idle at the moment) but really good. I love having the low down supercharger power, and it picks up a lot of power higher up. I've just done 100 miles at 70mph and some A roads and got 44mpg average (indicated) I get at least 400 miles to a tank anything upto 520 if on the motorway all the time.
Remap wise, you're looking at about 200-210 stage 1 and it makes it drive amazing. Mpg also goes up to about 50mpg on the motorway (did for me anyway). Someone described the 1.4tsi remapped is the same high up as a standard 210 2.0T but with faster/stronger pick up from low down (Ive never driven a 2.0T so cant compare myself)
As for 140 vs 170, the 140 is the better buy in terms of if its cheaper, but I personally wanted the exhaust showing so went 170 (it also has a boost gauge but I'd rather have a temp gauge than this) All depends on price, engine wise they're identical and both map up to 205ish.
Beyond stage 1 you can realistically get upto 250bhp but is a lot of money (turbo back, intercooler, induction kit, another map) then if you want more you can get a hybrid turbo or k04 but then you'll have to look at an upgraded fuel pump etc.