you have a nintendo network ID, so instead of random numbers you have like a username, when a player is in your room, you can view their nintendo profile and then send them a friend invite, it's clunky but still so much better than the friend codes system
in terms of the lag it's really not too much of an issue if you stick to 1v1, you can find a lot of relatively lag-free matches in that mode, though honestly it might be more noticeable to someone who takes their smash more seriously and plays with more precision.
yeah i honestly would not get a wii u *just* for smash, particularly if you have melee, project m etc. and still play them frequently. The main reason one would get a wii u is if you plan on playing the other exclusive titles too.