there is (exmpl) email@website.com . amail would be the part you want, @ you have to have and(if you have a custom email this can be whattever you want it to be) website.com is just advertisment....
As many as you can maintain. Many addresses are useless unless you can use them.
As many email services as you can handle, I have like 20 temporary ones.
there is two parts so you can get to it differently
(name of account)@(website).com