Anything over about 250/100 is overkill, but it all depends on pricing.

If they charge $5 more a month for 1Gb versus 250/100 then maybe go for it.

This setup doesn’t make any sense. You need to route all traffic from the ONT into a router, and then into switches and access points.

Any other topography is unnecessarily complicated and a losing game.

No harm, but usually we only do this for a specific reason. Like giving a network printer a static ip address so windows can find it more easily on a day to day basis.