Lift as often as you can recover from. Depends on the individual, and varies greatly especially as one gets older.
Increasing muscle mass is the absolute best way to lose fat. And at 280 lbs, with only 3000 calories/day, he will lose muscle mass unless he is lifting consistently imo.
Imo, only worth .02, being 230 lbs at 6' 2" is a perfectly reasonable weight; BUT, losing the weight gradually is key; and if he feels great and looks good after losing only 25, no reason not to stop.
Supplements? fish oil, and probably Vit. D; protein shake (peri) post workout (very important given his caloric restrictions)
p.s. insert all the usual caveats here about the value of interwebz advice, consult a doctor before embarking on drastic lifestyle changes, etc., etc.