I have flown a SEP 7 seater for 4 years, a SEP 6 seater for 42 years and counting and a MEP six seater for 15 years. Every aircraft is a compromise between price, seating capacity, fuel capacity with full seats, maintenance costs, comfort, etc etc. Used MEP aircraft are very cheap for a reason. Maintenance, airways charges, landing fees and AVGAS add up very quickly.
Older aircraft of the same type are usually lighter and can carry a bigger load than more recent models (thinking of my 1973 BE36 vs 2015 BE36). The basic airframe is the same but several hundred pounds heavier in recent models. I can carry 5x 170lbs standard adults with nearly full fuel. I have done trips to Ireland and Scotland with 6 adults on board (one couple was lightweight), we had minimum luggage on board and ample fuel reserves. UPS delivered all the suitcases we cared to ship directly to the hotel.
Without knowing your qualifications, typical mission or future aspirations, it is difficult to advise. Is this your first aircraft?