Hi GT you can get about a mile past the swans/slipway but it gets a bit narrow up there to turn a biggish boat.
Moorings wise, there are swinging ones just inside the harbour, but no 'marina' as such. Easiest place to stop is either just in the harbour on Mudeford quay, or a mile up outside the captain club hotel (good food too! ).
Main problem is the tide ......and the channel marks - if you are not in the right place you will hit the bottom. They put the main channel marks back next weekend - but the tides is very early - hence why I am out the following weekend- good tides all day. Really only come on a few hours either side of the either of the double high. Once you are 'in' you will be OK ( even if it means trimming up )
If you have aday in mind let me know and I see if I can head out to meet you .