I got the 4/128 model simply because it's impossible to get your hands on the 8GB models in EMEA, plus there was a 10% discount available and I had to act fast. I have not run out of steam and I have a similar usage scenario to yours, plus designing and printing models on my 3D printer.
I was a little worried about 128GB disk space but I use a microSD card, a NAS and the Surface comes with 200GB SkyDrive.
Awesome, I will save myself a good amount of money in the small one then. Thanks for the reply and help