Do the windows and Linux versions of bitcoinQT use the same wallet.dat file; i.e. can I move the wallet.dat file from a windows machine to a Linux one and have bitcoinQT work with that wallet?
Same question for the directories and files containing the blockchain data; i.e. can I move all the directories and files from the associated bitcoinQT directory which has an up to date version of the blockcahin on a windows hot wallet to the associated bitcoinQT directory for a Linux cold wallet to get that wallet to see the latest view of the blockchain?
The wallet.dat file is universal, it should work on all platforms.
The blockchain files should work as well, but both computers would probably need to be compiled against the same version of BerkeleyDB to avoid needing to upgrade (or downgrade, which may not be possible) them for the new computer. If you have the same version of Bitcoin-qt on both computers (and the linux version is statically compiled; if you're not sure, it probably is), then you'll be fine; if not, it should still work, if the versions are close to each other, but it's harder to say for sure.
I believe the chainstate files will need to be rebuilt by the target computer either way, unless you're talking about copying over the entire datadir in which case the statement about the blockchain files applies to them as well. Same goes for peers.dat, although that can be rebuilt extremely quickly so it's not something you really need to worry about.
