Acclimating in the rooms where it will be installed, is necessary, and the longer the better. Putting it in the garage would be a bad idea.
Yes, check the subfloor and the bamboo if you can. A pin type meter won't work. They make what are called non destructive meters that you place on the floor and the electronically measure moisture. Pin meters need to have the pins poke into the wood to measure moisture, but as I said, the won't work in your situation.
If the crawl space under your house has a well placed vapor barrier, your chances of success will be a lot better. Check with the flooring manufacturer and see if they approve of installing a vapor retarder on the floor before installing the product. I'm speaking of a craft like paper called Aquabar. It reduces vapor transmission from under the house, creeping inside the house.
Bamboo isn't really wood, but like wood, you will want to keep the heat and humidity somewhat stable..... meaning don't flip the heat off for two weeks at Christmas time if you go visit relatives.
What's the climate like where you live? You might get by with just acclimating. Not many installers here check the moisture, they acclimate the flooring.
Also, you probably need to sand the OSB seams.... Most are a bit higher than the rest of the sheet. You want the floor to be as smooth and flat as you can get it. Check the manufacturer specs on flatness. This is important so the joints don't flex when you walk in the floor.
