Dont worry to much about a pc laptop. I am running a I3 woth 4 gigs of ram 17". And i can do with it whatever i want. Only the initial android compiling takes ages, but after that still fast. If you also want to build for apple, you should look at a simple laptop with about the same specs. Anything higher would just be a bonus.
I will also be getting a Mac later on to build for apple.