You can get stop overs (and overnights) at Mevagissey, but its not the most visitor friendly place, especially for a newbie. You are only allowed in the outer harbour, the visitor moorings are on the big pier on the left as you go in. Be aware it can be a long climb out of the boat, and I have had more than 1 refusal to climb back down !
I wouldnt worry about Mevagissey, there are a lot of stunning places round there, my picks include Polkerris and if the weather is settled a run to Polperro where you can beach the boat right in the harbour on a beach. You can also run up to Fowey, the good news is that the tender pontoons are free for boats under 6m. A run up the river is also great.
As mentioned above, get some training, its the best investment you can make. Dont forget the safety kit, anchor, VHF and lifejackets as a minimum.