I have done a 18, 28 and 30 day voyages on Cunard as a solo. Have had a wonderful time. I do a large table, you get to know the other people and almost everyone does different things so there is always things to talk about. Have met a reporter who retired from the BBC, a actress who did tv and films and her stage actor husband. Great stories all.
Dont worry about the tours unless they are for couples you will have fun. And knowing your table mates can have its advantages, In Lisbon I did a tour, then was walking around the town looking to get on the cable car, seen a couple of my table mates who had all day tickets for it, and they got them from another couple who used it earlier. And they gave me them as they were done.
Have had lots of fun.
And the not talked about thing is you can do what ever you want when you want. But it is always what you do and feel.