Well, it just really depends on the horse & how well he adapts to things, don't ever set things in stone with training.
Your right with starting slow, especially if he's not been worked very much, and hasn't had much experience with lunging, especially with side-reins and the pessoa system. However, make sure your horse minds you on the lunge before using the pessoa, I mean, doesn't run around crazily and spook at just about everything...It can be very dangerous, and even when using the side-reins.
From what it looks like, it may take longer than you have in mind with the pessoa system, I mean, you don't need to be lunging more than 2-3x a week at most [like full-workouts] and when you begin in the pessoa, start with it very loose and only do it for a little while, so the horse gets the hang of the entire feel of the device, like the side-rein things and the thing around the hindquarters [can't remember what its called].
Do go in order with the 'level' of steps in the pessoa, start with the long and low. But if you don't plan on driving or dressage really, I wouldn't recomend doing the top setting...We do hunters at my barn and only do the bottom two levels, & possibly the third if its really needed...But then again, its your horse...If you've never used it before, get some help before you even begin to use it, find a trainer or somebody with experience with it, or you can end up with bigggg problems.
Not sure if that helps, but I hope so =] Just remember, take your time with things and don't push him too hard.