1) Ctrl+Tab i believe opens the chat. It's a little tricky right now. Either way you can change the key to open the chat for the options, for question 2) also.
2) There is a panel calling Rearming in the control options, on my keyboard it can be activated with LAlt+à, that key is the second to the right of L
3) I have no idea to be honest. In general tho remember to press LAlt+Enter when you load a game to switch from borderless window to real full screen for some more fps