Re: And the thrid ship
All three were laid down as battleships but the 3rd, the Shimano (note the M) was redesigned to be a fleet support carrier. It was not intended to be a launch platform for attack/defensive aircraft, but rather a floating repair station in support of the 1st carrier division.
The Shimano was never completed, but was launched. She was sailing, unaccompanied round the coast for fitting when she was spotted by a US submarine and torpedoed.
Interesting side note. Anywhere where dimensions for these ships are given are giving misinformation. The exact size was never known, only estimated from photos. The Japanese were so paranoid of spies that they were built in three sections, each with separate plans which were destroyed upon completion. Second interesting note. Rumour of the Yamato and Musashi got out, but not what they were, so the IJN published some launch postcards of two new light cruiser ships (Mogami class I seem to remember) using the battleship names.