I'm letting my little plants flower now too to get an early batch of peppers. I'm sure it will stunt their growth and as a result probably reduce my overall yield for the year, but I'd rather have a few up front and a moderate amount later in the year than none in the near future and a ton in the fall.
Then again I might feel differently in the fall when everyone else has a bumper crop and my plants are all still little. But well see.
I let one Hungarian Wax go to flower real early in the house last year and then saved the seed from the first pod. That way it was pure without work. Yes it definitely didn't produce well after that. (always have too many anyway)
You can let them go at the height they're at if you like. The plant might not even start pods yet unless it's getting great conditions. Cayennes should set fruit relatively early if they have nice conditions and they'll just keep on growing too. Not to worry, if you give them plenty of sun they'll grow nice and fast and your plant will be over a meter high with tons of pods before you know it.