A good 3D graphic card is a must for a CAD PC, so if you update anything then do that.
The processor cooling fan (as supplied with a new processor) is not worth upgrading unless you want a very quiet PC, or if you intend to overclock (which could well be a consideration in your case). As for the rest of the cooling solution, again, if you don't intend overclocking then 'normal' cooling will be fine.
If you W7 64bit, then go for 6GB RAM. This may well help with your CAD software as well....but that would depend on what software you use.
Personally (and this is only my opinion), I would avoid DinoPc. Do a search on these forums.
SSD drive? That's one option. Not a bad one either, but I don't know how much it will help with your work.
If you want an operating system with 3 licenses, then you have should purchase 3 licenses - windows 7 included. Otherwise you would be in breach of the license terms and conditions.