Character interactions - as many as you want! Sometimes I'm in the mood or its been awhile - and I'll do as many as 4-5 in one day. For a four day trip - I usually FP at least one - maybe two. I often pick either the Character Outpost at AK or Character Spot at EPCOT. Sometimes I FP Mickey at Town Square. And I often wait in the standby line at Pete's Silly Side Show as those lines tend to be short. I prefer "non-people" character meets as a solo. I recommend BB-8 and Chewie for SW fans. Kylo Ren was meh.
Character interactions at
MNSSHP - If you want Jack and Sally - pay careful attention to when their line is starting - and assume it will take a couple hours. I probably would not do another character interaction IF YOU ARE DOING THIS ONE doing this one during the party - as it takes a lot of time. In general - I limit myself to one interaction during the party. The lines are just too long and I have other things I want to do.
Character meals - in four days for a solo - if you have never done a character meal - or simply really want to do one - I'd suggest just one. At these - to get photos - you either need to make friends with the family next to you or hope the handler or a service staff person is around. I've had great luck at these if the family next to me is willing to adopt you - but I'm female - that might make that easier. I did have a good one with just the character handler and my server one time - but other times - it can feel awkward to find someone to take your photo. I'd risk this at Tusker House just because I love to eat there and I'd be okay with the character stuff doesn't work out. And if you did a princess meal - you could probably get selfies. For me - I'd never consider Princess meals or Cape May or Cinderella's Royal Table solo. I have to admit though - just to see the princes - I'm thinking about the relatively new one that has those (someplace on the BW).
If you love SW and are going solo - you could consider the SW Dessert Party. You'll meet other fans who will be happy to chat, can do the character meetings then, and it saves waiting outside to get a great spot for the viewing. Though - I think the dessert choices are meh at this one. A couple of the alcoholic drinks were great - but I can't drink much at one time. IF you aren't driving and can hold your alcohol well..... this one might be good for you. I chatted with a couple of fellow fan girls (about 20 years younger than me!) and a older couple (mid 60s) when I went. Saw the two girls the next day and we happen to end up chatting again in line at MK a couple of times. Their touring plan really lined up with mine - it was funny! There were a couple of solo guys at the dessert party I went to - but they weren't the strike up the conversation types. I think I was the only solo female.