FB ads - Testing for new products

Hello Guys, I need your opinion regarding something.

If you first run an engagement ad for social proof for a product and the numbers are good ($0.01 -$0.02 CPE), do you move to a conversion ad if you achieve no sales while running an engagement ad ?

when you go for a conversion ad what would your preference be a ATC conversion ad or checkout one?

and for the pixel to optimize perfectly for the audience and start selling properly, is a $5 daily budget over the period of 7 days for an audience of 10 million people a good idea, or you prefer running conversion ads with a narrowed audience?

you success and/or failure stories are highly appreciated.

thanks!