Q: are the cats more likely to give coins if they're happy?
A: Yes!
Q: do the toys and food need to be outside to attract new cats?
A: I don't think so. I have most of all of my food inside and the more I have the more cats come. I don't see a difference in cat amount with toys inside or outside.
Q: about how many toys per cat is enough to attract more cats?
A: Cats are attracted by both and toys.
Here's what the developer said about it:
Q: do the teasers count as toys if they aren't in use?
A: In terms of stray cat attraction I think they do but I've never the cats interact with it on their own. I put all the toys in one place. All of the toys were moved from that place except for that one.
Q: is there still a max number of cats?
A: The cap seems to be 21. I haven't seen anyone surpass it.
Here's what the developer says about it:
I'll edit this comment if i get more information or need to correct anything. I am not the developer and this is all based on my own experience so I might be wrong.
Bye! Meow~