i wrote a white paper on this exact subject a few weeks back. Rather than try and repeat the summary/details here, i think best to point you at the link;
one thing to note ref your question on GPU; is that the current release for azure we only support 2k12 os for gpu, and this is limited (due to a driver limitation) to a max of 20sessions.
We are working on 2k16 support, which will remove this 20session limitation and should be available soon. I will also update the white paper with new sizing info for 2k16 when its available.
let me know if you have more questions after you have read the white paper,
i thought i was keeping you busy with all my questions.... looks like you got your revenge by giving me that doc to read!!!!
thanks, this looks helpful.