I would have a few wondersuits, for newborns they are fabulous. Then while bubs is still little and the days are warmer just have singlet/singlet suits and nappies. Don'tget realy elaborate outfits. When they are a newborn, up to a few months old it is about comfort and ease of changing them. You can get really cute singlets and bodysuits at the moment
The general rule is what you are wearing plus one layer. to check how warm bubs is feel their chest.
My dS was born end of march when it was very hot in SA, he wore a singlet nappy and a wrap a lot of the time at home, except at night.

Good luck. I know it seems scary but you will figure it out.