Yes, you can. It's another question if it makes sense though. What is your site about? Would ecommerce ads fit rather than informational product (ebooks/guides/courses) ads?

It's better to focus on one thing than spreading yourself too thin. Throwing every kind of ad at your site might just make it look spammy and you end up with no revenue.

I agree. I guess it really depends on how targeted your traffic is and what exactly you're site is about.

Include both Adsense and CPA is ok. However it is not recommended to monetize too many advertising if you are promoting specific product or you are selling your own product..you don't want to distract visitors concentration from clicking away through advertising like adsense.

Yes, but be sure not to give your visitor too many options to where they are simply confused in regards to what to click on. Then you might not make a conversion at all. I would suggest taking the most profitable monetization method and use it.