I've used Tru-Oil on knife handles before. The number of coats will depend on the wood type. A dense oily wood like cocobolo will need fewer coats than something with more open pores like wenge. With a hand rubbed oil finish, it has enough coats basically when you like the way it looks. You can put a couple coats on and the wood will be protected, but may still have the appearance of open pores with some woods (the inside of the pores will be coated with finish), or you can continue applying coats until all pores are filled and the finish is perfectly smooth. If you do a few coats of spray on poly on top, you wouldn't need as many coats of oil because it's just there to inhance the appearance instead of providing full protection. The poly can be used to finish filling the pores. As far as a spray finish on top of it, I'm not positive with Tru-Oil, but I think it would work as long as it's good and dry first. I did a similar thing with tung oil recently refinishing a bow for my son. It has a maple riser and I put either 2 or 3 coats of tung oil on it, can't remember which, sanding back down between coats. On the last coat, I rubbed it in real good, then used a lint free cloth to wipe the excess of. That gives a nice satin finish by itself, but I went ahead and sprayed a couple coats of satin poly on, mainly because it's a one piece and I figured the spray poly would work better than tung oil on the limb glass. It came out pretty nice.