My cat is usually very shy and quite the loner, and has never been affectionate toward anyone. Today, she's been clinging to me and sleeping on me all day. Does this mean kittens are on the way?
This could very well be what it means. Cats get social when they are getting ready but the best way to tell is by how many days she has been pregnant. Cats are pregnant for about 65 days. If you think she is close and she is being social, she is probably getting ready.
Yes, she needs a private place to deliver. What kind of issues did she have delivering the first time?
Will you consider spaying her after this litter? It's not healthy for female cats to have multiple litters or heat cycles. She can also get pregnant again within a week of delivery, which is obviously terrible for her body.
Previous issues she had was a kitten getting stuck in the birth canal, and she wouldn't move them herself. We were planning on spaying her, but by the time we could afford it she had got outside and pregnant again. The other female is spayed, and the two males are a bit too young. Hopefully after this litter we can afford to get her spayed and the males neutered.