What is happening with the grain?

[king casey]

I tell ya casey, after a hard day with the sandpaper, your'e partner will think you are moonlighting at Baker's Delight.

cheers, Mark.

[McCreed]

Don't forget to get grain filler when you go to the Big Green Shed.
Timber Mate is probably what most people use (myself included).
The colour of the filler doesn't matter since you're going with a non-transparent finish.

This my unsolicited advice, so take as you like but...

personally, I would get my paint (acrylic lacquer) from an auto parts supplier (Supercheap, Autobarn etc). I don't know you'll find acrylic lacquer at the BGS and I've had poor luck with the enamels they sell, but YMMV.
I (and lot's of others) have had good results with Duplicolor base coat and Septone clear coat (rattle cans).

Also, you'll want to take it down to P240 after your grain filling and before your primer/sealer. 120 is still too coarse.