1, No, a 'Compass Rose' is what they call the centre face of a compass... you know the north/south/east/west with all the pointy triangles bit? And it's quite a clever name really as it combines the 'rose' bit for a flower class corvette and the nautical part name. Clever!
2, The IMDB page says "The Compass Rose was played by ex-HMS Coreopsis. She was given the number K49 in the film which was the number of HMS Crocus (sometimes wrongly thought to have been used in the film). The real number of the Coreopsis was K32." and "When the film was made in 1952, no Flower Class corvettes remained in Royal Navy service. The ship used was therefore the Greek corvette Kriezis, brought to Britain for scrapping. She was already scrapped by the time the film premiered."
http://www.imdb.com/title/tt0045659/triviaSo to simplify, the COREOPSIS (K32) was sold to the Greeks who named her KRIEZIS and when they were scrapping her, the film makers bought/borrowed her, re-named her the cleverl 'COMPASS ROSE' was given the random number K49.
There's a story that during filming with the merchant ship crew, the MV COMPASS ROSE passed a US battleship who was on a visit to UK waters. There was a signal exchange that went thus, (I paraphrase):
US Ship: 'what ship?'
Compass Rose: 'K49 Compass Rose sailing the cruel sea'
That's surposed to be true... read it in a 'famous signals' book.
3, I'm pretty certain that KA was a shore base for training RN or RNVR officer types.
4. don't know.. I could probably guess... but if we wait, one of the 'more knowledgable' will be along soon and will knock us off our feet with his briliance.
I watched 'Enemy Below' the other night and ahave a raft full of similar questions.. if I remember them* I'll ask them later.
* I'm getting on in years.