Prime with Zinsser BIN primer---it can be tinted to the color you choose. The beauty of using the BIN is that as long as the surfaces are dust free, the primer will adhere.

Easiest finish coat will be acrylic enamel(water based).

Get a 1&1/2" tapered brush---I use Purdy brand----and you can cut in(paint the lines between ceiling/wall or trim/wall). The technique is to wet about 1/2" of the tip of the brush with primer/paint, and wipe off the side that will be against the surface you do not want covered. Slowly and steadily draw the brush along the line, painting only the trim/wall about 1/2" wide.

This technique seems to take a long time, but it is actually much faster than taping, painting, untaping, and repairing the job. Any mistake is easily cleaned with a damp paper towel(I use the blue work towels sold in rolls at HI stores.)

Another avenue if you want a smooth wall or textured finish is to roughen up the paneling by sanding lightly by hand, mesh tape the seams, and simply skim coat the grooves and mesh tape with joint compound similar to finishing drywall. Mud the seams and grooves first, let dry, then skim coat the whole surface with your last coat using a topping compound. Sand smooth between coats and texture if desired or leave as a smooth wall finish. For a smooth wall finish you will have to be more careful sanding going progressive from coarse to a fine grit paper using light to spot defects. Prime with two finish coats color.