I currently only have a 400 watt Amp so it was reccomended that I get 4 gauge wiring at Futureshop. Later on down the road I would like to upgrade my amp and subs. Would I run into any problems using 2 gauge wiring with my shitty amp so that I won't have to get new wiring in the future?

 

No problems at all. Except for fitting big gauge wire into smaller gauge inputs on the amp.

 

fit big gauge to smaller amps is why they made bussbars and fuse blocks.

My moto is the bigger wire and more of it the better.Go to here to figure out what will do your needs in the long run.the extra cash at the start is worth it in the long run
Recommended Power and Ground Cable Sizes

 

like these guys have said, it's always good to think ahead. I always hated having to go back and re-wire, mind you that was way back in the mid 80's. I learned quickly to go big from the get go, you can always reduce at the amp end if you have smaller amps for now.