Language Question

Hello,

I'm an American (Orthodox) who was interested in spending an extended period of time in Eastern Europe. Serbia, Belarus, and Russia all come to mind as possible options. My question is from a language perspective, would Serbia/Serbian, Russia/Russian be better from the perspective of getting a handle on Church Slavonic?

I don't know the first thing about these language families so starting with the Cyrillic alphabet it will all be new to me.

Can Serbians understand Russian and vice versa, or ?

Thanks for your help.