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.

Just out of curiousity what would an estimate be for the cost to buy lvl 90+ MN engineers (BVE or EBVE) and repairmen?  I tried looking around and couldn't find any prices.

Prices aren't really found on the forums. NF's trade is heavy on the barter, and all you need is a general idea to make sure you don't get ripped off. You can get some idea looking at the trade tab and noting the lowest ones that don't sell. Start by undercutting that by at least 10-15% and work to an agreeable price from there.

I can say that, considering the going rate for a level 12 boosted elite "neut," a single decent level 90 with vets and experts it's going to be several tens of millions.

Richelieu is an excellent ship, it can easily do 100k+ dmg every battle.  Get a few good engineers and manage your OH time well, you should be able to go 44 knts. Speed is everything for MN.  And UK/MN is always agressive play style, if you just sit back then you went the wrong nation. Of course rush at proper timing is important.