Is the Russian "П " the same as the spanish "r"?
So I am a native spanish speaker and I noticed that the russian r sounds very similar to our r, but I can't tell if they pronounce it like a singular "r" (like in the word arbol) or like a double r (like in the word carro)
It is Р :) П is pronounced similar to p in papá.
The sound is similar to that in arbol. It is normally a two-tap R. The word гитара makes it pretty clear. Russian does not have any other R's , so if you make it longer, in does not matter. You will just sound less natural (the longer you make it, the less natural it will sound).
Note that it does get devoiced before a pause and (partially?) before devoiced consonants. That does not matter much for being understood, of course. As I said, Russian only has one such sound.