If I wear NCR armor will I still gain rep with other factions? Also is their a limit of how much rep you can get with a faction until a point? I have done quite a few NCR quests and I am now liked but when doing more quests I don't seem to be gaining anymore rep?

I'm trying to role play as a NCR soldier.

If it legion or brotherhood no they will attack you as they are sworn enemies of NCR and yes there is a limit idolized is the limit.

Wearing faction armor practically turns off the rep system. I don't know that it prevents rep gains, but I wouldn't be surprised.

Then you will enjoy Giskard's new mega-mod - it lets you actually join the NCR and work your way up to 'Ranger Elite' (the guy on the game package).
http://www.theengineeringguild.co.uk/
Regards