Oil paiting requires often to let paint dry for a while and reworking the shadows and highlinhts, or détails to be worked out after sufficient drying of the main colour, like free hands, or détails like on flags. Therefore paintings several flats at a time is useful to provide this drying time, to occur without dead time. Looking a figure in process after one week often gives new judment, defects, weaknesses that are not visible one all is done on a row. So yes, painting 3 to 4 flats , usually two large and two 30mm size seems to be better.
More is despersing attention, as I usually "enter" in my characters, to try to give thm a personnality. When too many are started, most will remain unfinished on the table in a corner and will never be ended !! It would be like writing weveral books or building too many houses at the same time.