Cave chose X360 because MS courted them heavily, they liked the hardware and someone at Sony said something disparaging about their games early in the life of the PS3.
RE: sales, there's this quote from Asada, circa 2010:
Asada (Cave): Because our specialty is danmaku shooters, we must have many different modes. Furthermore, we must produce sales for these arcade port and systems as well. So we must evolve and adapt these games to the home system and make them look really flashy. We must please veterans without alienating the beginners, and we must please beginners without betraying the veterans. All of this must be done with strict budgets since we are only producing the game for the XBOX360, a system that not many people have. We must sell at least 50,000 copies of a game. If we don’t, it is a failure. These are the hurdles we must clear.
There's also another interview that I can't find right now where they said Deathsmiles did ~50k in Japan and ~200k overseas. EDIT: here it is
—Right, so this is like a test case for a new model of Cave game.
Asada: That’s right. The idea for making a game like this goes all the way back to Deathsmiles. When I joined Cave and we started our X360 development, the first game I participated in was Deathsmiles. It turned out to be a big success. Our initial target for sales was only 10000, but in the end we ended up selling 40000 domestically (50000 if you add the platinum collection version), and another 200,000 units worldwide.
—Wow, I’m surprised to hear it was so popular overseas!
Asada: The world and setting of the game was really well received. It was especially popular in Europe.
In the context of crowdfunding, there's no sense concerning yourself with post-launch sales before they've even proposed a product--there are a zillion factors to consider when analysing sales data that become more or less relevant based on the platform, the delivery method, the price, the marketing, etc.
(The reason they kept flip-flopping on region-locking their games wasn't to cut off importers, it was because they thought it was important to cultivate an international fanbase beyond the one that already exists, and the most effective way to do that was to enlist an international publisher that's better equipped to push your game in those markets.)