Sand it. Both to give the surface some groves for the new paint to bite into and also to smooth out any bumps and whatnot. Spend more time where you stopped stripping the wood so it blends nice. The more time you spend sanding, the better your finihed job will look. Oil based primer is recommended for any bare wood. If you suspect the paint on there now is oil based, primer all of it, if not, just the bare wood.