From Potter Heigham there's Hickling Broad not far at all, but it means going under the bridge, so unless your boat is short enough you'll not get there by river; it's a nature reserve and is just lovely

I wouldn't suggest heading south of Great Yarmouth (across Breydon Water) in the time you've got. Places you should try and get to: Wroxham and Horning. Mooring in Wroxham can be a pain, try and get there mid to late afternoon before everyone else: It's mostly stern on I think. On the way to Wroxham is Salhouse Broads which (used to have) a beach....
I'll point out at this point that I've not been on the broads in a few years...
...Salhouse Broad is a lovely Broad, on of my favourites.
One thing I will suggest: Get a good map, and make sure you have the induction from the guy at your boatyard...piloting 50ft of cruiser down a river is rather amusing when you don't know what you're doing...
And stick to the speed limits on river. There's river police everywhere and they love nothing more than screwing up peoples holidays. The reason for the strict limit is the wash from boats trvelling at excess speeds is starting to wash the banks away

Usually there'll be a rev counter with a rough guide next to it for translating engine revs into speed. All speed limits on rivers are in MPH, not knots, so thet keeps it simple.
Oh, and on a rather lower tone...don't use the toilet on your boat unless you have to...they stink after a matter of hours and 'pumping out' the tank isn't a pleasant task for anyone

Most staithes have public toilets on them, or very close by.