Hello,
Personally you don't need a ton here. Whenever I configure CRM I put everything on a single box and work from there. Do you have a machine powerful enough to run SQL and CRM etc together?
I wouldn't worry about speed so much as having just enough memory and patience if your hardware is slow.
You can then limit your SQL to 4 gigs and then allow your IIS + OS to use the rest. I've run entire instances etc (on the fly) on a cheap laptop from BestBuy and installed everything there.
Another option would be to use a VM in Azure, but for the roughly 300 bucks a month lol (depending on if you ran it 24x7) you could buy that laptop with 8 gigs at Best Buy... or get some 12-16 gig machine from best buy.
That's my suggestion.