Re: Compatible? Good?
1) If you do end up going for an Asus motherboard I'd recommend the P8Z77-v series
2) Yes, for 3 reasons;
No. 1 - You'll save money in the long run, a lower PSU now would cost (lets say) £50 and then upgrading later would mean paying £80, whereas you could just pay £80 now.
No. 2 - It gives the option of SLIing, and the only thing better than 1 670 is 2 679s (or 2 680s/690s/7970s etc. :P )
No. 3 - It's more efficient. Not only are higher end models made with 80+ efficiency but also, the less power a PSU uses the more effective it is
3) That's ok, just be careful when re-installing the OS on the SSD
5) The RAM will be fine, so long as you're using 1600+mhz (it doesn't need to be, but it would be a waste not to)