Please see the Popular Classes section of the SYC Dinghy Racing Overview page.
Being on a tidal estuary, dinghy racing takes place at different times based on the tide. See the online SYC Programme for details of this year's race programme.
There are SYC organised dinghy cruises (with safety boat cover) about 10 to 12 times a year spread over the summer months.
Probably - but it depends on the size and class of your boat.
More helpfully, you should get in contact with the SYC berth marshall.
More information on berths at SYC can be found here.