I have several teams of 4 level 50s in the swtor. My latest team is at 41 and is 3 vanguards and one commando. All can be DPS if desired and any vanguard can respec to tank. The commando is a good healer, but an awesome ranged DPS!

I 4 box weekly operations with one of my teams just fine. They all are DPS and my guild provides 2 healers and 2 tanks. I routinely do TFB story mode in this way.

I can solo most HM flashpoints which will get you geared in columi in no time. After that you are ready to do sorry mode ops to get Rakata.