"There are many options for what you need and modelers all have their favorites. I use a water based matte polyurethane exclusively, the brand I use is MinWax as a primer sealer on all wood surfaces. I coat most parts and surfaces as I progress with the build. This poly seals the grains and acrylic paints apply and adhere nicely. In addition all glues that I have used adhere to surfaces coated with this poly…including CA glues and PVA glues.
One exception is if you plan on staining a surface, determine how you want the stain to look before treating the wood. I normally stain a surface before applying the poly. The stain takes on a richer, deeper, tone when applied to untreated wood. However, you can control the stain saturation for lighter tones by treating wood first with a sealer (not the poly) that remains porous once dry…look for what is called “sanding sealer” again MinWax being one brand readily available. Sanding sealer seals the wood grain but allows stain to penetrate into the wood rather than puddle on the surface. Sanding sealer is designed to help control the depth of penetration of stains thus controlling the tone. Once stained, I apply a finish coat of the poly.
One more caution, in every case natural unfinished wood is very slightly darkened with the poly application. I have never found this to be an issue especially with lighter toned wood such as bass wood. The slightly darkened tone is actually a better look. I use the poly to specifically achieve this richer tone.
If you are looking for a primer paint for all surfaces under acrylic paints, especially metal parts, there is also an acrylic primer paint available by most paint lines. It is normally neutral grey in tone with a flat matte sheen although I have seen it in creamy white. Acrylic primer is specially formulated to have extra surface adhering ingredients. Whatever brand of acrylic paint you choose look for a corresponding primer option. I use simple craft acrylic paints and use the primer for that line. I have found that for water based acrylic paints a water based acrylic primer works best. Also, primer paint tends to be thicker than regular acrylic paint so use caution when apply the primer paint that you smooth it out and do not fill in details.
Last comment…the poly noted above also acts like a primer for your acrylic paints. I use the poly as both a sealer and a primer under acrylic paints on all wood surfaces. I use the grey acrylic primer paint on metal surfaces. In addition, when you paint or stain a surface you can use the poly on top of the paint or stain to provide additional surface sealing and a finish coat. Poly over acrylic paint gives the paint a deeper, richer, tone as well as protecting the finish.
Just my experience and preferences but I hope this helps…