The marina channel should have about 1m at low springs, was silting up a lot last year with the heavy rain early in the year driving muck down the rivers feeding the harbour. However they did a lot of dredging last year so the channel should be a bit deeper this year. In terms of coming out of the inner harbour towards the outer harbour - opposite the Harbour Masters office - you need to be on the harbour Masters side where it is deeper. At the bottom of a big spring, trim your leg up and you should be ok. The harbour motuh narrowed a lot last year as the sand spit from the Gimblet Rock side spread out, the tide does sluice through there now, its a bit narrow and you can get standing waves in there which looks daunting, but just plough on and as soon as you get outside the harbour mouth it eases off very quickly.
Check out the marina website www.hafanpwllheli.co.uk
for details of the marina itself, and dont forget to pick up a marina handbook with the local tide table in it, collect one from the marina office.
In terms of the local bays, as you come out of Pwllheli there is a row of yellow bouys markign the bathing area - pick up the leaflet from the marina office which shows what they all mean, otherwise you may get your collar felt by the local authority beach patrol boat.
Llanbedrog has a drain pipe for surface water sticking a long way out, I would suggest talking a walk on the beach at low tide to find it and check the Admiralty chart, i know one or two people who have hit it and its not pretty to see a leg hanging on by the shift cable!
Abersoch gets very very busy at peak times, lots of yachts and otehr boats - I try and avoid it as its just not fun. More than happy to meet up and talk you through the local charts for good places to go and areas to avoid.
What are you planning to do on the water, cruise, ski, donut, fish or just laze around and enjoy being afloat?