I just read this thread:
https://forums.505go.com/discussion/36127
I have a reverse question: what happen if I add some 1* to my roster? My PvE and PvP will be affected somehow?
Not really. Only the top end of your roster affects scaling. Pad out the low end as much as you want.
Ok but how many tokens of my top end affects scaling? I just sold a useless Silver Surfer and I will not want to open a Legendary Token for a while… 
PvE events are now almost impossible to win in the latest matches: enemies are almost unbeatable with level over 200 against my team composed by 2** and 3*** around level 100…
I have Heard the top Three characters on your roster, i.e. the highest level team you could take into a given game. No idea if that is right or not though.