To heat your space, you'll need just over 1300w to raise the temperature 350 over ambient. If you went with 2000w, you'll reduce heat-up time and have better control over fluctuations. You can get 2k heater elements pretty cheap. At least on this side of the pond. You'll only need one.
As far as the rest of the parts, I suppose it depends on how deep your pockets are and how accurate you want the temp.
