1) Submitting variants increases your equity footprint in search results. Meaning that the more ad slots you take, the higher the chances are your ad gets click on. If you limit the variants, you will start to get less equity, and thus less clicks.
2) You can exclude variants in Google Ads, by subdividing it down to item id. Here is the documentation: https://support.google.com/google-ads/answer/6275317?hl=en
Then exclude the products you don't want to advertise for.
3) You can't exclude product in the feed with your current tool. However there are lots of feed management tools out there that have the ability to exclude based on rules.