No, gmail does not support variables, so you can not put something like {{firstname}} and expect gmail to populate it from your recipient name, this will be a great feature though.

Canned response is still a lab which are not supported by google support, we would suggest you to turn your gmail labs off and on and see if it works for you.

you can create predefined messages as shown above in G Suite or Gmail which works well for basic template needs, for advance template needs you should consider application at google apps marketplace

Yes, you can create a filter based on your criteria and apply a canned response to it, this will give you auto responder functionality

No, though you can access your Gmail emails in MS Outlook via IMAP or Google Sync tool, but canned responses only work from within Gmail on web.

Yes, it will work even if you use Microsoft Outlook with your Gmail, because each email first hits your Gmail and will trigger your autoresponse.

It only works within Gmail, not on phone, but there are some third party tools which you may consider as they work on phones too, we would recommend you to explore google apps marketplace

Unfortunately not, gmail does not provide this functionality yet of adding attachments in predefined messages, but you may consider inserting google drive links to make it work

No, there are keyboard shortcuts in Gmail for email actions and you can see them by pressing SHIFT + Q in your Gmail, but gmail does not support keyboard shortcut for canned responses yet