I have kept my Leisure 23 on both the sea and the Norfolk Broads, so I will add my 2p worth.
In general, you really need a bill of sale or receipt from the seller. Otherwise you have no proof that you own her. I never bothered with SSR, but I never went anywhere other than coastal waters...
I used to keep a log in a notebook, but since I moved to the Norfolk Broads, I don't generally bother. Seeing as I no longer use charts, VHS radio (I do have a hand-held just in case), or GPS (except as a speedo), a logbook doesn't seem necessary. I can guarantee that few of the hire craft...
When my boat was on the Blackwater, I didn't consider it a proper sail unless I had gone aground at some point - usually when returning to the mooring.
I have a Tab A, and am very pleased with it. Don't waste your money on the Samsung case. It is about £50, and mine is breaking up after only about a year.