Excellent idea!

Le Havre hull
P24 guns
KM AA 

yeah. like adding a twist to the game. it's a revitalization.. XD most people stay in games that "personalize" their own ship. they can also add a camo slot. so it would be personalized. 

And make it submersible !

the ideea sounds nice, but what about crew?

 i take first example

Yamato Hull
Lion 2 Bridge
Kaiser Guns

will you need KM gunners for sure, but what type of suport you will need: IJN or UK? 

For BB7, it be better that all parts will come from Every nation. but the sailors to be used will be aligned with the BB7 BO. 

BB7 BO is IJN, All parts of All nations can be used, but Sailors inside will still be IJN. Gunners be IJN. there is no limit to what guns can be used. you can use BB 1 - BB6 guns. depends. the point here is that BB7 will be a fully customized and personalized ship at your disposal.  

remember! you can do what you want. in all systems with interchangeable components, always one (... only one) system will be THE BEST.
following this idea, all players will always choose this configuration.

in this case your personal configuration is no longer personal, but a 'must be'

next question: how strong should be the result of this personal ship design? between BB5 and BB6 or stronger than BB6?
There's already the EBB5.5 class between BB5 and BB6. stronger than a BB6, in GB battles this ship would outclass all ships smaller than BB6.

to insert different sailor's, different AAA, HH, different armor and so on, offers enough possibilities to personalize a ship. btw ... I personalize my ships with an original name. lol

Not All possibly. the point is to enjoy the customization. it's BB7. You wont get to that within a month or 2. it will take some time. and by that time, you can recognize what you want in the game. you cant possible generalize that people will just use the optimal. that's why it's fully customizable, also with limits. you cant mount everything into a single ship. you either choose, light ships, heavy ships (of course bb6 hulls will accommodate everything) but the point here again. is to have fun in creating your own personal designed ship which will banner your playstyle