Hi I think you would be better to fix then paint , you could give a first coat if you wished but the ceilings / walls will rarely be straight flat enough to get a perfect fit. After fixing you will probably need to fill the abutments with caulk try not to make this to thick then leave overnight and then emulsion the ceiling edge and the coving , then cut the emulsion in to the wall . Light colours are easyier than dark colours but the best way is to use a good quality sinthetic brush 3 inch . load the brush and start cutting in about half an inch from the edge and gradully get closer but stop short of actually cutting in . Leave this dry fully and on the next pass cut in fully . With the skirting knot and prime before fitting , fix to the wall and fill any holes and caulk in , if the walls are a light colour then undercoat the skirting and slightly onto the wall , then emulsion and bring this down onto the skirting , apply a second undercoat and then gloss .
Hope this helps a little Pablo