I have the exact same boat,same color(1974 23 potter Tsunami).Why not use the Perfection on the topsides as well? It's much more durable than the Brightside and it won't cost that much more.You can add a flattening agent to it as well.
I like the System three Quick Fair for filling nicks,dings, gouges, and screw holes.It's epoxy based and cures fast and sands easily.
If the topsides are gel coat you could spray them straight with perfection and no primer.
I sprayed mine with a two part urethane made by Epifanes,it's similar to other urethanes like Imron & Perfection.
My hull was the original red Seacraft gelcoat,and in good shape structurally, but it was faded.
I prepped it by first de-waxing it then a thorough sanding with 320 I sprayed two coats of interlux epoxy 2000 white primer followed by a sanding with 320 paper.
I then sprayed it with the two part Epifanes urethane.I shot two coats on it rather quickly the first day,let it cure overnight then sanded it again and finished up the next day with two more coats.
I'm a rookie sprayer but it came out nice,a few spots with some orange peel and one sag,so I had to sand and buff them out.
If yours has been painted you'll need to find out what was used so that you can make sure you use the proper primer,some are not compatible with certain paints.
I'm on the third year with this paint,and it still looks as good as the day it was done.If it was me I'd use a two part urethane like perfection on the entire boat,shines forever and wears like iron and is extremely fade resistant.
A few pictures of mine showing the finish.