Small random-orbit or pad sanders make this job go faster. (Wallis first covers these boundaries with Synkoloid patching compound so no edge is visible after sanding.) As shown, you want to make sure that there is a feathered, smooth transition from exposed wood to old paint. For areas that might get close scrutiny, you can follow up with a 100- or 120-grit rubdown to erase any scratches.
That said, depending on the composition of the paint, some exterior paint is appropriate for painting the interior of a home. Paint meant for the exterior of a home will hold up over time.Just be sure that the area being painted is well ventilated, as it will come with a strong smell at first, which will dissipate over time.A painting professional will be able to advise you about whether your exterior paint is appropriate for indoor use.
