at this point selling rares you have more then 6, sounds good for me.
you might need the cash for building decks.
quick info for t50's: they are the deck from players in the weekly highscore, played by the ai.
the decks are changinh every time a t50 player safes a different deck on his account.
so t50 is changing all the time. sometimes there are plenty of farms (because the most players in t50 are offline), sometimes you hardly catch a farm, because the most players are active.
t50 resets every sunday on 3 am gmt.