Stoavio, IMHO if it is just hurting from lack of use, and as you say you have led a pretty sedentary life, suck it up, there is a difference between aching and injured. Although with a back from what I surmise, sometimes you cant tell the difference. It will get stronger, but it will always hurt. The chiro on my route said the human back is only made to lift 50 pds...so you use your legs, and your power zone to reduce the stress on the back.
As far as a back brace, it does nothing but reinforce your back, and can actually cause you to get hurt far worse when say at home you need to move the couch and you dont have your brace on and your back is used to having it on, and SNAP.
Like I said before, do nothing else if you want this job the first couple weeks, except rest for the next day, and avoid anything else strenuous like.........well you know.
And this is JMHO