Assuming that the pock marks and gouges are from the handling of the wood, and not the wood itself.... Are the pock marks little tears from coarse cutting tools? With a well selected piece of wood, you should not need a filler. You should be able to sand the wood smooth. I think I recall Pine sometimes liking to load the abrasive paper, not necessarily gumming it up, but the dust not wanting to leave, like balling up, and making it more difficult to get a smooth surface. Kauri is especially bad like this, very soft, but yet, very slow to sand to a nice finish.
There are many ways to get a black gloss finish. Personally, for black, I use the Chemcraft lacquer system, I use industrial tints in their wash coat ( which is actually intended for metal, but works really well for this) Industrial tints can be mixed for whatever color you want, black ( you could put in a teeny drip of red to make the black more 'black') Then the wash coat is sprayed until you get the black, then top coat in whatever sheen of lacquer finish you want. Some of the high gloss, black pigmented lacquers are nice too, but may be a little trickier to get an excellent finish with. This technique can also be used in say, the Pratt& Lambert Clear 38, which is a decent, hard drying interior varnish. I would stay away from water based finishes, and stay away from 'spar' finishes. The clear 38 will tint with standard tints.
A regualar, interior, gloss enamel will also work well. Oil paint should ALWAYS be thinned, unless you have a specific reason why not to thin it, and IMO, you will know that reason when you are ready for it. ALWAYS thinned. Work out of a paint pot, not the can. It is impossible to load a brush correctly from a can. That is a whole different story, but the gist of it is that the brush is lightly dipped, the very tip only, the specific amount of finish you want to 'carry' with that 'stroke', and the brush lightly pressed against the sides of the pot. Scraping the brush against the lip of a can is a self defeating technique, fro applying paint, it is useful for removing paint from ther brush, not in loading the brush. This will take some time to learn, but is absolutely worth learning if you work with a brush.
Always thin oil paints. Naptha is a faster solvent than regular paint thinner, Turpentine is known to flow a little better, but I cannot use it as I have become sensitive to it. Regular paint thinner would be the most common choice. Japan drier is very useful for oil paints, just a few drops in your half cup or so mixed finish for a coat or 2. The pot life with Japan drier is up to 24 hours, and at 24 hours, you will feel a slight difference in handling. Do not put mixed paint back in the can.
A thin coat of thinned paint, quite thin for the first coat for better penetration, Japan drier for better, faster, more complete drying, will sand well. It may sand better than raw wood, depending on what wood. Another slightly less thin coat, and more coats, sanding betwenn coats. Keep it thin, use Japan drier. Again, do not return any finish with J. drier in it, to the can, it will ruin it, dead. Sand, and recoat with thin coats. Thinned maybe 30%, maybe more for the first coat. Very thin coats with J. drier, can sometimes be wetsanded in a few hours.
If you are inexperienced with a brush, foam brushes may be easier.
Hopefully the piece of pine you chose is less resinous than pine can be. Sometimes there is to much resin, but you should be abe to see this. If it starts looking like resin pockets, that is no good. If it looks like nice, straight grained wood, you are in good shape.
With wetsanding, and thin coats, you can get a brushed finish that will polish out , and be as glosssy as the most glossy of sprayed finishes. When you get the technique, even the brushed coats towards the end, will look like sprayed coats. No problem with getting a full blast gloss with a brush. Thin coats and wetsanding, even coats, and be careful about runs.
As you progress, wetsanding with 600 grit is good. Let the finish dry enough between coats.
forget water based finishes for a really nice gloss.
If water based finish is necessary for some reason, you might think about black transtint dye, in shellac, over the bare wood, then adding (not too much) standard tint (black) into a waterborne poly finish. Test your technique first. Latex paint is a very poor choice. The water polys, like 'Stays Clear' or, ' Enduro', for a more industrial oriented water poly, ( that was my favorite one, sprays nice) would be what I would choose for a water based black gloss finish that was meant to be handled, like a guitar neck.
Hope this helps
. It's a resinous wood - makes it smell nice, and burn nice and hot in a campfire. On the other hand, since the wood is saturated with the resin it can be tricky to finish, and you wouldn't want to burn it in a fireplace since as the resin burns it releases nasty (flammable!) stuff that you don't want in your chimney. 
