Helpful Hint for Freeplay Mode - While not a guide for this achievement as such it'll simplify and streamline this achievement.
Beat every level on story mode to start with which will unlock 4-LOM for purchase (buy him asap). Make sure you have him and Darth Vader in your party when in Free Play mode. Why? To save a LOT of switching between characters.
4-LOM - Can open Bounty Hunter (Boba Fett), Astromech (R2-D2) and Protocol (C-3PO) doors, can grapple, isn't a bad blaster character (with dodge ability) and can throw Bounty Hunter mines.
Darth Vader - Can manipulate both types of Force, throw levers/switches, constructs build-its and can open Imperial (Stormtrooper) and Sith (Darth Vader) doors .
Between these 2 characters the only things missing are access to shortie passages (like Wicket), the ability to jump really high (like Jar-Jar) and R2-D2's thruster ability and the game will include someone to fill these gaps for you anyway. The only real downside is that Jawas will zap 4-LOM and render him motionless for a few seconds but that only applies to a couple levels anyway so it's not too bad.
CREDIT - a mate of mine who doesn't play online
, couldn't give a damn about achievements
and isn't even registered with TA