Hi Liam,
Sorry for the delay in responding.
I live in Broadstone and my boat is currently on a swing mooring in the creek at Rockley.  My email is 
john.edwards@live.co.uk if you want to get in touch.  Very  happy to meet-up and go for a little sail if you would like.  The only trouble is that I am away on holiday from Wednesday for a week, so anytime after that.
Concerning your initial queries.  The aft berth is pretty small and I would suggest only suitable for one adult or perhaps 2 small children.  Others might think differently.  I use it more for storage, spinnaker etc.  I tend to day-sail, which in this area is great fun - the lifting keel is very useful in Poole!!
Not really an expert on the ups and owns of the mast; only done it once, but I bought the boat from 2 ladies and they said they did it regularly.  I am sure others can comment on the ease/difficulty.
So far, touch wood, no major dramas with an older boat, except to replace the outboard, which despite being serviced regularly, seized-up on me and was not really economical to repair!  The usual annual activities, replacing ropes etc, a new sacrificial strip for the foresail, repairs to the dodgers etc. but nothing you would not expect. 
Hope this helps