I think you have a good start w/ plan. Agree lots to do at Watkins.
Glen SP is a must
The restaurant right at Village Marina in Watkins is very good - outside seating and you can't get more convenient
Jerlandos - good italian food, Crooked Rooster - brewery & restaurant next door is good, Garcias for Mexican.
Stop by Sampson if you have time - we're in slip 99. Seneca is very busy this weekend due to trout derby but if you need / want I could probably find you a slip at Sampson as a couple of folks aren't in the water yet. I'll PM you my phone # just in case.
B'ville is a favorite stop but sometimes the upper wall is totally filled by locals that come and leave their boat on Tue - Wed to make sure they have a spot for the wkend.
Seneca Falls is a nice stop and a good but easy day trip from B'ville
Best swimming holes are - the bay just off Frontenac Is on Cayuga (listed as springport cove on AC) sandy but water temps are nasty this time of year.
Clear going in past spar buoys - just avoid the extreme N side of the entrance. This is a favorite anchor, swim, stay o'nite spot.
N end of Seneca as long as there isn't a S wind
Goose Watch winery (Cayuga)has a good dock - its on AC Lat N 42-46.057 Lon W 076-46.015 There are others but haven't been to them and not sure about docks from 1st hand experience.
There are lots of restaurants in Ithaca but a while since I've over there.
If you are having a good time on Seneca you might consider adding one day and skipping traveling the length of Cayuga for one night - save it for another trip. I think you'll like the Finger Lakes and be back... Seneca is the cleanest swimming water you'll find anywhere close by but it takes awhile to warm up as it's 625 ft deep! Last week temp was 44*F week before was 38*!
Have a good trip and call if you need any more local info. Good bunch of folks at Village marina - Seneca Sail & Power Squadron and Finger Lakes Yacht Club members - just say Hi and ask for info.