I believe you can play the main a lot, even uni. I sail 2-up but do the main, I never cleat and play the main with about one arm length. If you need more you're not depowered enough. If you only need one, playing the main becomes a lot easier. (sometimes I have to head up a couple of degrees to keep the trim with one arm length, but it is definately possible). But steering up al the time, makes the boat heel more and loose speed. Speed is definately key.
If you find the main to heavy, get yourself a good tapered mainsheet and you'll notice the difference!

Secondly, most difficult when sailing uni is that a lot of boats around you are sailing 2-up. Sail your own course. Upwind I tend to loose a bit on the 2-up teams, almost same angle but a bit slower. Downwind you can make up for that.
Last weekend we had about 15 knots. A guy weighing 72kgs sailed a 2007 Blade. His boards (long ones) were about 30cm's up, cunningham almost maxed and rotator pointing to the crossing of beam and hull.
His sail looked more like a windsurf sail then a catsail, that is the point you need to be at between 15 and 20 knots.
Try to trim your sail in light weather on the beach. Measure how many cunningham you need, where the rotator should be and how hard you should sheet in.

Gill