Email aliases do not give you anonymity. An email address or alias is always an identity marker.
Aliasing helps to easily compartmentalize your online presence. It enables you to easily track who’s sharing your email address with whom. You can very easily shut down a source of spam, because you have to change it at most for one online account, when retiring one email alias, instead of all of them.
I’d recommend to create a new email account, one you pay for, with a provider that includes an aliasing service for it.
Assume that at least half of all services you have accounts with, will remember your old address. Decide on a case by case basis, what is more desirable to you: Keep your history with a business or start from a clean slate with that business?
For having multiple phone numbers, there is only VOIP. I can remember there is JMP.chat as a provider of multiple numbers. The problem is, those numbers are often not accepted.
Another idea would maybe be to have your own PBX. All your numbers would be obviously be grouped together in sequence, but you could still give every business you work with a dedicated number.