Hello!
I’ve only been playing the harp for a few weeks and I have only taught myself the very basics of the piano, so my opinion might be different to those of other peoples.
But I think it would help to learn the piano after learning the harp. Besides the technique and how you play flat and sharp notes, it’s the same.
You don’t really need to mark the C and F, but it probably would help. I remembered them by making words which relate to their position. They’re strange, but they helped lol
D = Defense, because it’s ‘defended’ by two black keys
B= Bottom, because it’s at the bottom of three black keys.
F= Front, because it’s at the front of three black keys
They must be quite similar because when I first started, even though I had already had one lesson, my Mum was a lot better than me because she can play the piano. The only thing I was better at was the hand technique.