On my SS commuter bike, I have a disc front and V rear.

To avoid wearing down the rear rim, I almost exclusively use my front brake only. If I anticipate a hard brake coming up, I lightly touch the rear brake to get a feel for the point of contact and stay prepared.

I'm doing a pretty good job, as my rear rim is very clean (something it never was for more than a day or two when I used it all the time).

So yes, all you need is a front disc, unless you're a downhill racer or if you want to use a rear disc to avoid rim wear (which is wise).