The minimum number of engineers at BB4 level is 4. Unless you have god-tier ones, this holds for every nation. And for Richelieu, yes, the only things you have going for you are that all your guns fire forward, and that you can go 44 knots. The Rich is best played like the PBB Dunkirque: wait for a distracted opponent with no support in range, then rush in and fire away. If it gets hairy, use your speed to beat an equally hasty retreat. Try and focus on enemies with high angle guns and long hang times, and do twist and turn while engaging.