It depends. Basically any clarity is fine if eyeclean, although this can depend on various factors and the size of the diamond, larger diamonds sometimes necessitating a higher clarity in the cushion. Sometimes some SI2 can be eyeclean and perfectly fine, but you need an expert vendor to advise you and also to have your own comfort level of ' eyecleanliness.'
Colour can be more visible, so according to personal taste, so I would say to go for a higher colour and lower clarity if eyeclean.
Both are to a certain degree. You should be able to find eye clean SI1 cushions. Maybe even an eye clean SI2 but those are harder to find. Colour depends on your sensitivity. My guess is that H and better is fine. The larger the stone, the more warmth it will show. However, some people just don''t see colour and don''t mind I/J stones.
it totally depends on what is important to you. some people are color sensitive and others are very clarity sensitive. some are both. you have to decide what is most important to you.
i would be remiss if i didn't mention that cut would be the most important factor. a well cut stone will sparkle so much that it can hide color as well as clarity. a better cut of the same color/clarity will look obviously better than the poorly cut counterpart due to the sparkle.
Yes, basically if you do find an eyeclean SI1 clarity for example, it will look the same as a VVS if no inclusions are visible, assuming everything else is equal. Colour on the other hand is visible or could be, so generally that can be a greater consideration according to your own personal taste and comfort levels. It is up to you how you prioritise the ''C''s to find your diamond.