Do you mean learning them side by side or one after the other?
EDIT: Ooh, sorry you already said in the title that you want to learn Estonian after Finnish.
If you already know Finnish, then I guess it will be much easier to learn Estonian, than when not knowing any other Finnic language at all. Although it can also make you to mix them up most of the time, especially if you don't know Finnish well enough.
I can manage,
trying to learn,
unfortunately, slowly fading away