It all depends on what type of feel you want from the neck. Definately use linseed oil on the fretboard unles your going to put a finish on it as well. If you want something that has more of the oil fininsh feel as opposed to the thick poly finish i reccomend a wipe on poly. Its pretty thin but puts on enough of a layer for a little extra wood protection.
Well i have found personally that with oil finished it catched the oils from your hands too much and gets sticky. You can by a wipe on poly that is gloss so it will give it a good shine without being as sticky and a spray on. I have personally used that on my bass neck and its amazing. If your looking for something thicker and have a good sray gun you could go with a nitro laquor finish. I have that on my 6 string and it has a great feel and its very easy to spray, clean up, and maintane.
No don't put the oil on at all unless you have an oil with a stain in it and want it a specific color. With the poly put a coat on every 3 to 4 hours and you want about 8 coats. The instructions dont say to put on that many put i reccomend it for a little extra protection from impact. I personally dont put more that 3 coats a day because i like to give it a little time to cure but its up to you. Not use OOOO steel wook on it in between every coat to rough up the surface so that the next layer will adhear better and use it after the las coat to smooth it out.
If you were going to use sand paper i wouldn't go lower that 1000 grit. The problem with sand paper is that there is always a focal point of the pressure and you run the risk of sanding through the layers. Ive mever tried it with sand paper because of that but you might try it. If all else fails you sand off the rest of the finish and start again.
No problem. If you run into any problems hit me up with a message and ill be more that happy to help.
Dont use steel wool if you use a water based poly. No matter how hard you try you will not get all the metal dust out and it will rust. On a maple neck you are going to see it.
Ive used steel wook countless times and never had a problem with it. You just have to wipe it off with a dry towel before applying another coat.
Good idea. Try a couble different finish types on some scrap wood and see what you like before you do it.
Quote by guitar-tin
what to use if i use water based poly?

3M makes these gray colored scouring pads. They work just like steel wool (actually a little better). You can find them at auto parts stores, home depot, etc.