Hi!
I have an RB750, which has been running perfectly for quite a few years now (and still is for that matter). I've just ordered a hEX (RB750Gr3) to replace it and I now wonder if I can use a backup from the old device to get the same configuration without any problems? Or do I have to set everything up manually on the new device?

You can use configuration export not the backup. It is recommended to edit exported configuration, there can be i.e. some MAC addresses You don't want to transfer to new router.

Never found an export function..? Decided to take screenshots of all the configurations and then set everything up manually on the new device. More work, but opportunity for clean-up and improvement. Thank's for the reply anyway:)

The export function is available in command line interface, and the output of the export command is a sequence of command line commands. The command can be directed to a file. To get to command line from Winbox or WebGui, press the [Terminal] button.

I suggest using "/export terse" as it makes every line of the output executable on its own, without relying on previous lines.
(Of course, dependent objects still have to be created in the correct order.)