Im a painting teacher/ signwriter,
and I do stuff like this often
My advise would be get your piece of wood first sell it with an acrylic seller/primer, under coat, sand once cured ,paint againg in acrylic undercoat
sand back to a smooth finish , By this stage the pours in the wood will be some what full and the porousness sadicfied , then coat in (now this deepends weather you willl be finishing in acylics or enamels) enamels for enamels , acrylis for acrylics, , so coat in under coat suitable to finish,
sand back using fin grade paper, then use a filling compund suitable for you wood , either 2 part epoxy or a plaster style filler , epoxy is bext is you arnt familliar with the materials,
once filler is dry sand back to desierd smoothness, you may need to reaply the filler depending on your first go,
once sanded smooth paint in a suitable under coat , then start on you disiers finish, ,
Sorry about speeling but I hope that helps, also dont use wood putty as most are made with linsead oil and will blead
hope that helps some what