Are these all OK?
(I am watching or doing something right now)
If I say;
It's really enjoyable watching you. / It's really enjoyable to watch you. / It's really fun to watch you.
It's really enjoyable doing this. / It's really enjoyable to do this. / It's really fun to do this.

Question

Are these all OK?
(I am watching or doing something right now)  
If I say;
It's really enjoyable watching you. / It's really enjoyable to watch you.  /  It's really fun to watch you.
It's really enjoyable doing this.       /  It's really enjoyable to do this.        /  It's really fun to do this.

Answer

All of your examples were perfectly fine, though usually I would make myself the subject of the sentence:
I really enjoy watching you (play the piano, or dance in the recital).

Answer

I would say;

'It's really fun watching you.' (but it sounds a bit creepy out of context !)
or 
'I find this really enjoyable/fun' 
'It's fun doing this.'