I agree with all the things luxxeon said.  Learning to model is very useful if you wanna make your own models, which you already do.  The thing about sculpting stuff is that you get a really heavy mesh, and sometimes you can reduce the polygon count, but most of the time you have to use it as is.  Unless you know how to create detailed maps from the surface, and use them on a low poly model.  Most people don't know how to do that, I don't think, and make it look as good as the high poly version.

Bsurfaces in Blender is the best way I know to paint polygons over a model, but you're right, it does take some understanding of geometry to get a good result.  Stick with it though.  I mean, it may be frustrating, but keep at it.  As long as you don't have anything better to do at the time, it's not a waste.  You'll eventually learn it, and at least be able to get a result you can use!  That will make it all worth while right there!  Don't worry about keeping it all squares right now.  Try to make them all squares or quads, but having a few triangles in there won't hurt anyone.  Sometimes you have to.  Ngons subdivde bad, so keep away from anything with more than 4 sides, and you should be fine.  That's easy to do.  Just knife cut any polygons that have more than 4 sides, and make it into less than.

Stick with Blender!  Don't give up.  It's free, and it's just incredible.