I have to say this NOW ! STOP & SLOW DOWN ! I see your getting excited and wanting to pull the trigger, DON'T ! You really need a careful and thought out Plan and then get suck into it as your going to build up your system over time as funds allow it. Without a plan and careful consideration you will end up spending good money after bad and from your opening post, you are not in a position of having "disposable cash" to toss around.
The Valence Batteries may sound good off the top and they are okay BUT your not gaining anything other than used batteries with a reduced lifespan that may or may not be good and have an unknown lifecycle remaining. Someone above mentioned the 280AH cells which you would need 4 to make a 12V pack, plus a BMS that comes out to $510 USD with S&H, Taxes & Duties plus BMS say $150... $660 all in for 12V/280AH compared Valence at 12V/120AH for $500 ? do the math.
You need to define what exactly you want to do, how much you are willing to budget (hopefully they come close) and then works towards collecting the bits & pieces to put it all together. Also something to keep in mind, and NOONE MENTIONS IT ! is BOS (Balance of System) which is breakers, fuses, wires, switches etc... that stuff adds up amazingly fast s add 25% ON TOP of your budget for such items, I would say say budget 30% to be on the safer side.