Ugh, when we lived up there we had rats coming into the crawlspaces in the winter…took a while to figure out how they were getting in (a botched plumbing job by a former owner left a gap into the sewers) and the worse part was trying to get rid of them since they never came into the rest of the house, so our cats could not get them and we had to resort to poison…NOT something I ever want to have to do again!
Meh - silver fish are harmless. While kind of creepy looking, it’s not like they bite your toe off or something.
As for the no-see-ums, just hit the hardware store and buy the screen material that is woven tight enough that they can’t get in. We did our whole house a few weeks ago and it’s made a hell of difference - worth every penny.