For my PBA-4 I used Timbermate to do the grain filling and that is available at that big green shed. I used a Timbermate color that closely matched the natural color of the body
As for the Nitro primer I got it at the same time and from the same place I got my Vintage white Nitro. Same for the clear gloss Nitro. Sydney Guitar setups. Yup, the Nitro cans almost cost as much as the kit, well, it certainly felt like it did.
Only did one coat of the primer. Got 4 coats to the body out of one can of the Vintage white, and then 3 coats out of one can of the clear gloss due putting some clear on the neck.
Timbermate, (really rub that stuff into the grain.)
Sand
Primer
light sand
color
very light corrective sanding
clear gloss (point where I jumped to light finish buffing)
level sanding (1500grit up to 8000 or more grit)
Finish buffing and polishing.