You have plenty of options when it comes to controllers but personaly I much prefer Ethernet than USB for it's reliabilty and most of the cheaper ones are USB.

Software like John pointed out is one thing to bare in mind has you may want to factor in the support base out there. This Depends on the type of person you are really, some need lots hand holding others just like to get on and figure it out them selfs. But the true test is when you have problems that are not user error or lack of knowledge. IMO nothing comes close to Mach3 user base in this regard.

Personly I'm not a Fan of planet software and found it a little basic for me but others like John have no problems which is all that matters in cutting terms. I also don't like being tied to one board or make of board.

Mach3 will do anything the others will do regrards Cameras and surfacing mapping etc because they are just special macros or scripts which are written then tied to the screen set. Thou I don't know of a surface mapping macro I'm sure there will be one if you ask around. If your handy with coding then get writing has it shouldn't be too hard.

There also Linux CNC which should seriously be considered and will work with the PP and I believe 64bit.? But don't hold me to that.!
It matches and surpasses Mach3 in lots respects, esp with the PP side of things. It's the Geeky user base that becomes a problem and lack of quick support that often puts people off, thou I do believe it's getting better!. OH and not to mention Linux OS it's self which puts folks with little PC knowledge off.

To be honest think if on Budget and you know your way around PC's and dealing with OS's and software then I'd have a serious punt with Linux Cnc has it's free and very capable software.!