Just a comment about the mention of Stella Models... I ordered 2 kits there, both very well packed, in tip top condition, quick communication to their clients... And a good price too! So I recommend buying it there!
And in regard to the 201 vs. upgrade pack 201, all you get in the upgrade pack is a body, reinforced gears (not lightweight gears), carbon battery plate, lightweight motor plate and a lightweight body.
If you feel the lightweight body is REALLY going to help you get the best out of the car, get the upgrade pack
Otherwise, I think you shouldn't. The carbon battery plate is more bling than functionality really. The reinforced gears are cheap to buy seperately and not every user had problems with the original gears to start with. The lightweight motor plate (this version at least) I heard is (relatively) prone to bending and like the original motor plate has a bad seal with the gear cover. A better motor plate has been released already (#54276, shown in
this build) to make a better seal with the gear cover, is developed to be stronger yet also still is more lightweight than the original. There is by the way no wing included with the body, so you still have to order some stuff for it together with the tires of course.
So what I'd do is get an original/stock 201 if you can find one NIB, and with the money you save buy a body, LMR wing (which is a lot thicker and tougher than the Tamiya ones), reinforced gears and ceramic diff balls
If you go full out on it, also buy the new battery plate with the better seal (it will save you changing a spur gear and pinion within 25 runs), ceramic balls for the thrust bearing of the diff, Associated springs (the TRF ones give only 3 options in stiffness and the discrete dot of colour coding at the edge of the spring easily wears off) and perhaps the LMR brass front suspension block/weight (running on clay, I needed 45 grams of weight behind the servo and some other setup changes, including a change in roll balance, to get the understeer out).