You can add as many as you like. Boiled linseed oil does not fill the grain, but it does seal it. It will shed water but the open pores that aren't filled can still accept dirt and grime. Usually wait 24 hours inbetween coats, but don't let it fool you; once you rub in a coat its dry to the touch after taking all the excess off... letting it cure over night or longer is the trick. If too many coats are added it will bleed in the sun and you will def know if you screwed up, and its always a good idea to wait a good while before you take it out in the sun anyways. Boiled linseed oil does not get glossy unless you sand up to 1200 grit and get a real soft almost mirror finish type of wood... and even then it wont be glossy like a fresh coat of tru-oil, gloss poly, or gloss epoxy. Just take the bottle, put your hand over the top, turn it over and get some on your palm and then rub it in. Rub for about 5 minutes on each side thoroughly, wash your hands or wipe them off then go rub it for another 5 or so, then wipe the excess off with a soft lint free type of cloth.
If you want a glossy finish and something that will fill the grain with enough coats, use true tung oil although its kind of thick and can be messy. You can also try minwax tung oil finish which is tung oil with different chemicals added in and it dries faster, and with enough coats gets glossy. Most of this stuff is just about how many coats you apply but boiled linseed oil is the easiest finish to apply.
EDIT: Oh yeah one more note. If you're going to stain, don't use a minwax stain. Minwax stains are oil based and even when you wipe the excess off and let the stock or wood dry thorougly, when you go to rub on a coat of blo it will take a lot of the stain off and lighten the stock up not to mention it will be on your hands it can ruin it... use a rit dye stain.