You might be interested in checking out my SUL/XUL Enclosed Shelter Comparison article and the spreadsheet associated with it.
To directly answer your questions:
1) All three will provide enough coverage. The Gatewood should provide the greatest amount of protection due to it having full sides rather than a short beak like the other two. That said, used properly the other two are fully capable of keeping your gear dry - you simply shift to the non-door side of the shelter when it is raining. The beak on the hexamid can pretty much solve the issue as well. You could also use a much stepper angle on the cricket beak/entrace to provide much greater rain protection. So, honestly, all three should perform their job properly. Oh, and lets not forget... there is a reason that hiking gear has DWR ;)
2) Trying to get us to do the leg work for you eh lol (gigle)? Visit their websites and the math yourself ;) (though it would be nice if these cottage companies actually listed their square footage of room). But in the end remember, it is not always about the math. All of these are going to be about the same - but what really matters (AFAIC) is the "usable square footage". To me, the Hexamid feels like it does not have a lot, but it usually seems to have enough for my gear. To me, the Gatewood feels like it does not have a lot, and every time I get in one, I continue to say that. To me, the Cricket seems to have that "bump my head when I sit up" feeling, but it does seem to have a nice bit of usable sq footage. Plus, it all really depends on how big you are (both height and fat). At 6' all of them can feel small when the weather is really bad and you are all holed up inside of them. But hey, guess what, that is what comes with a "solo" shelter! Hikers concerned about room inside of their shelter should by a 2 person shelter :-D
3) I have never had the Gatewood setup in strong wind... but I would put it in this order: hexamid, cricket, gatewood. Remember though, the hexamid can take up to 10 stakes, thereby adding additional weight for the additional guylines and stakes. Forsake not the terminology "Total Shelter Weight" - but at the same time, the Hexamid is the lightest enclosed shelter that is out there and worth buying I feel. You can have it fully setup at 354 grams (12.48 ounces / 0.78 pounds) and that is saying something!
Something to consider: you should included the "SMD Skyscape X" in your list. For an additional few ounces (ok, and a lot more money than the cricket/gatewood) you can have yourself a fully enclosed shelter. At 425 grams it is the definitive of a SUL solo shelter - and possibly the lightest fully enclosed on piece total shelter weight shelter in the world! I wrote an article on it that could be worth reading. A bit more money, a couple more ounces - but all three of your above questions would be nullified by going with it.
Hope some of this helps!
John B. Abela