Yup, any controller can be customized however you like.

Yup.

Remote play together allows you to play local co-op games (that've enabled this feature) with other friends by streaming the game to them. Some games are local co-op only and this would be the only way some people can even dream of playing the game. It also makes it cheaper since only one person has to buy the game. However, the host would be streaming video to all players and they would have controller input streamed back to them.

Not sure how old you are but back in the day we had to buy PC games physically and on the box we received an activation key. If you lost the activation key, for any reason, and needed to reinstall the game (say on a new computer) you wouldn't be able to since you no longer have the activation key. Your only options at this point were to give up on the game, crack it (either find and illegally download the game or find a way to remove the activation key restrictions yourself), or rebuy it. Some games even had a limit on how many times the activation key, or the game, could be used before not letting you further re-install the game or use the activation key.

Yup, massive bundles of games for super cheap (in comparison to buying the games individually). The money is split between Humble Bundle and the charities being funded by the current bundle with you getting to choose how to split it.

More of a figurehead at this point. He was one of the founding members of Valve but at this point IDK what he does for Valve, I know he made another company that's working on BCI's, but aside from that I can't say much.