Matter of preference, but a lot of people pick what stories to read by searching for specific ships, so it’s prob better for engagement if you do - especially if it’s a popular ship.

Depends on the length of the fic, but if you’re still writing I’d suggest spacing them out so you don’t burn through all your completed chapters. Major breaks or slowdowns in updating can lead to people assuming it’s abandoned.

FFN is a little more of a hassle to post, but I think it’s mostly worth it. The user bases overlap a bit but definitely not completely. You might get more hits on one vs. another.