well i am certainly no authority on BBs...here is my experience
i used the engies i was readying for the ss5 for my BBs
i never had above a 32-33 speed...up to nagato...the engies were a yellow, one elite, a base 9 and a base 10...all BVE by the nagato and ss4...
as i completed my ss5 max 120 run...the engies became levels 118, 117, 116 and i sold a level 117 cheap(base 9) and replaced him with a base 11 level 103...reps were at 116 and a level 91 i developed lateBase 11 and 12)
now as i drove nagato and fuso and even B65 to the yamato, the engies that would fit allowed speeds around 36-37 on these ships
on yammie, i have found that the 4 engies produce 39 knots with only bulge and 36-37 knots with some paper deck plating(yah yah i know, but it has a purpose of life extension so i can be more aggressive)...and those same 2 reps produce a fairly speedy healing rate...
the other slot is for the scout...
i would think hyuga would have those seven same slots for support.....and QUALIFIED engies and reps could be used in a 4 engie/2 rep combo with a scout
additional reps could be placed in T slots, but i use phh(never leave dock without it)
for what its worth...this is my experience with ijn BB lines up to yammie