The old fort is interesting on the main island but its tiny and can be done in 30 mins including walk up/down. Bon Bon beach can be easily accessed via dive boat - in fact one often dives in the general vicinity there.I need to contact 3P to find out if they will accept walk in diver. If they do then it will make the planning a lot easier.
Thinking to mix this trip with DIY sight seeing of the island. 10 days with 5 - 6 days of diving.
Sunset Cove is a bit isolated.
Town wise I much more preferred a visit to a village in Corbador island for example (great diving around there btw).
There is often a dedicated boat going to town from Sunset Cove so one can always get a lift, otherwise lots of local boats going to and fro.
But depends indeed on you - if you are an avid hiker the main island is bigger indeed, diving wise I found the Alad Island to be perfectly central.