At this time of year I'll guess it's going to be a head race (timed over distance, not side by side racing) where's it gonna be?
I'd suggest that you get on the ergo and get used to 20 minute bouts of effort at about 85% of your maximum, although it's important to maintain correct technique or you'll bollox your back in no time at all. Perhaps 3 times a week and get some recovery in between. if you want to do some weights on the legs, back and get some sit ups in to increase your core strength then that would be very beneficial. I'm assuming that you're already reasonably fit due to the cycling, but rowing uses up a lot more oxygen IME and can get you blowing pretty quickly – I usually find it's my arms that suffer afetr a long time out of a boat.
If you're racing as a novice then some more time time is a necessity as it's gonna hurt if you don't get some time to row in a crew and get some technique down in the boat as well.
Most important thing to do is enjoy the sport – if that's not there (either through getting it right or the craic with the crew) then it's all going to feel like hard work. I don't go out much nowadays aftre doing it for 20 odd years, but when I do it's like riding a bike – once learned it's never forgotten.
Rich