I'd personally keep him in work rather than giving him a break. Letting him be a lawn ornament can stress him out since he's already been taken out of his regular routine.
Lunging him with tack on is a great start, allow him to adjust to the weight of a heavier saddle. You're first few undersaddle sessions should involve just walking, lots of transitions, and allowing him to understand some new leg & rein cues. Really concentrate on maintaining rhythm, at all gaits. Don't worry about circles and serpetines and all that jazz at the trot for now, he's going to have a hard enough time establishing his rhythm and balance going in a straight line
. Once you feel he can carry himself independently at the trot, you can then introduce poles, circles, serpetines, some basic lateral work, etc.
To sum it up - transitions, rhythm, straightness, balance
Cantering is a whole other ball game, so that should not be introduced until he fully understands what you want at the walk & trot, can carry himself correctly and he's not leaning, pulling, hauling, bolting, whatever. The canter is not really a "gait" to a fresh ottb, they walk, trot, and gallop. He'll most likely haul you around like a freight train and try to gallop, not because he
wants to run necessarily, but because he'll be completely off balance at the canter, and if he runs, he'll be more comfortable. So once you eventually introduce the canter (could take weeks, months, depends how his progress goes) keep it short, sweet, and STRAIGHT. Pick up a few strides down the long wall, and back to trot, few strides down the long wall, and back to trot. You can gradually increase the amount of canter strides as he becomes more balanced. Once you can canter rhythmically tracking left, then you can introduce the right lead using the same process.
Also, reward, reward, reward like crazy