Zorbeet, do you prune them? I understand that they will have bigger blooms if they're pruned. Not cutting back each branch, but cutting away a few of the canes completely so that the energy is focused on the remaining branches. Some people thin away a third of the branches/canes yearly. Just don't prune too close to cold weather, or the new growth will be damaged. Keep in mind that you can have fewer, bigger flowers or more, smaller ones. Like you, I like the big blooms.
Your really young plants will probably bloom better when they're a little older. Yes, fertilize, but not too late in the summer, or you'll have a growth spurt that could be damaged by frost.
ETA: Quick Draw Sojita beat me to it about the pruning!