No paint in the join areas. And you don't need/want grain filler there - that's just for paint/finish. Both PVA and Titebond adhere to the cellulose in the wood, so putting any paint on the contact areas really weakens the joint. I normally tape up to about 1mm from the edge of the areas, so the paint will go over the edges for strength/adherence, but you minimise the amount of gluing area affected. The bottom of the neck is the main glue joint as that's the surface you can tightly clamp together, with the sides providing supplementary support. You'll find that the glue acts as a lubricant, so the neck will slip in a lot more easily than it does dry.

I bought a cheap pop-up toilet tent for my outdoor spraying booth. I've now made (badly but it works) a square wooden frame for it at the bottom, so I can have it on the patio and not just on the grass.