I'd recommend creating original content instead. It gives you many more monetization options.

There isn't one "best" platform. It depends on your budget. Flippa is great for variety, while Empire Flippers is better if you're spending a larger amount and want more verification.

It really depends on the industry. Meta Ads work exceptionally well for impulse purchases, while Google Ads still dominate high-intent searches.

I wish I had read something like this when I first started freelancing.