Just a point about the term flagship.
A flagship is the ship which the Admiral commanding a naval force is commanding from it is not the most powerful ship in the fleet. It may be but there is no particular reason why it should be. There were several cases in WW2 of an American fleet commander using a cruiser rather than one of his battleships or carriers as it was more convenient, during the cold war the Americans had several command ships designed for a fleet commander but completely unarmed. At Trafalgar the franco-spanish flagship was a 74 while the Santiasma Trinidad a 130 was present (Coincidentally the British flagship Victory was the most powerful British ship), at Jutland the British flag was the Iron Duke not one of the more powerful QE or R class battleships.
It just bugs me the idea that flagship = most powerful ship. The Coaltongue looks quite badly set up as a flagship it seems to lack cabin space for an Admiral and staff, also it seems to lack the masts for good signalling overall the fleet command would be better placed on a more traditional Risuri ship. Also the Coaltongues tactical role seems likely to take it out of the fleet and out of position to coordinate the battle line.