As soon as you hit the 2 front gun ships, you're speed will increase significantly. As far as the lower tiers are concerned, I have little opinion on them, as neither are exceptionally fast.

Regarding support sailors, I'd recommend going 5 engies/3 reps or 4 engines 4 reps along with AA, main gunners, scout and BO. Don't aim for a lower tier ship, it's a huge pain to grind up more sailors once you reach a higher level.

Yup, Angus has got it right. But if you like speed the only option is 5 engies. That is what I run. I did Corbet line, but Bretagne is similar in that they are VERY slow. Both lines meet up at the Strasburg, and with 5 engies you will be happy with your speed. Try to get Elite or +12 base for all of them and boost if you can. Also try to keep engies at the same lvl as their ability stacks better that way. Your Repairmen or 2nd set of gunners can play catchup if needed. But focus your lvling on those engies.

FYI: Since you like speed, good choice on MN nation. That is what it is all about. Rush in, Fire, Rush out...or...Speed away from thier rush and gain some range as you run. You will always have the worst range, but it can be overcome with skill.

4 engs are alright but you could use another. 1 rep will bite you in the butt I suggest you get more than 3.