1) It should be doable on the existing FD. The question is whether or not the Lower Limit screw will push the Derailleur out that far - that would be my only concern.
2) From a 48 to a 50, there shouldn't be much concern about chainstay clearance, unless that outer ring is really close to your chainstay right now. Buy the crank from someone that has a good return policy - or see if a Local Bike Shop has an extra 50T ring lying around that you can just stick up against your 48T to see how much further it sticks out.
3) The RD won't have any issues. The limits on the RD would come into play if you increased the Cassette's gear below 32.
4) Seriously consider borrowing or riding a bike with a 50-11 combination to see how much more top end you really get. That just seems like a heck of a lot of work for 2 more teeth.