Being in fresh water, you should need to paint less frequent than those of us in salt water. Here's what I've done over the past few years, it can give you something to go on...
After stripping the bottom down to gel coat after I bought the boat (June, 2009), I painted with 3 coats of West Marine CPP ablative, launched on July 2nd (it took nearly a month for me to remove the 19 years of hard paint and prepare the bottom after buying it). I had it hauled a few days before Thanksgiving, and the hull looked fantastic. I did a few spots of touch up last season, mostly to address some "cracks" in the paint. I launched mid-April last season, and hauled the first week of December. When I checked the hull after haul-out I only found one small patch of barnacles (covering a space of maybe 4-5 square inches). I did have some problems with slime last year, but a little uneasy reaching with a soft bristled brush on a long pole took care of that.
When I inspected everything last weekend I could see some spots where the gel coat is starting to peek through, particularly on the rudder.
I just bought a gallon of West Marine PCA Gold (made by Interlux) as practical sailor gave it a pretty good review, particularly on slime prevention. I am going to try and get two new coats on before launching this year, and hope to again go 2 seasons before needing a fresh coat.
edit: if you look at my avatar closely, the dark spots on the bottom are the spots where I touched up, should give you an idea about how little paint was applied the 2nd season.