I live on the edge of the Broads National Park. We hire the odd dayboat but never overnighted. There are various locations - lots around Wroxham or the Horning on the Bure side or up to Potter Heigham.
Or you can go south on the Yare.
It depends a bit on what you want to see - the northern side tends to be busy from the start of the season to the end.
The Yare side to the south generally has a higher proportion of owners from Brundle vs. rentals and you can go into Norwich if you want. That said 7 nights is probably enough time to see most of it just check the terms to see if you're allowed to go through Yarmouth - the day boats from Acle are not usually allowed to head in that direction.
Also check if the boat is able to go under the bridge at Potter Heigham - most are under a pilot but not all!
As far as boatyards go there are many - check trip advisor for how they compare and if they have parking etc.
Our most recent trip out was an afternoon tea cruise on Moorhen from Eastwood Whelpton - if you can sail then they're probably the best boat yard. Amazing boats some 100 yrs old!
If you can't Moorhen is a lovely but tiny classic motor cruiser - might be a bit tight for 7 nights.
www.eastwood-whelpton.co.uk