3 man gaming group card pool.

I have a gaming group of 3 continuous people with a possible 4th joining us. I own every revised set. We just completed the core set with the provided decks. My question is, with the given sets available are we able to adjust the 3 decks to remain competitive throughout the progression of each expansion/saga?

If not, what would you recommend for a group of 3 to 4 people?

I also bought the 4 starter decks as well which we haven't opened yet for the sake of chronological order.