It depends on where you live !!!
I live on the northeast coast so its still very cold here, even in April. I generally start setting away (veg seeds) at the beginning of April, onwards. As for my flower seed I start in January in the house, then move them into a heated greenhouse as things multiply.
I don't begin planting out until May - using cloches/fleece to help keep coastal winds from giving my plants a battering.
Can't see any problems with the way your thinking. Your doing everything right IMO.