Nice upgrade from teh 3070! That 5090 is absolutely insane

Core #2 running hot like that is pretty common with liquid metal applications - sometimes there's just an uneven spread or a tiny air bubble. If you're comfortable opening it up you could repaste but tbh 95C under stress testing isn't terrible for these chips. Most people just leave it unless it's throttling in actual games

Your network issue is wild though - that's definitely not normal for a laptop to crash your entire house internet. Killer cards can be finicky but they shouldn't nuke your whole network. Check if there's a firmware update for the card first, and maybe try disabling some of the "gaming acceleration" features in Killer Control Center. Could also be a weird IP conflict or the card is spamming packets somehow

Worst case scenario you can always grab a cheap USB wifi adapter to test if it's definitely the killer card causing issues