state ur budget and preferences (switch colour/size,etc2)
if ur saying layout, some are non standard.

Check my siggy for the last unit of Quick Fire XT, it's standard layout.

<Also are the keys on all mechanical keyboards standard? I mean can you interchange them?>
Keycaps have standard mount, you can swap it around. But, mkb keycaps do have different profiles. The original keycaps (OEM profile) come with a new keyboard do have 4 rows. Each row have different height/profile.


[attachmentid=7498792]
Row 1 (Pink color row), Row 2 (Blue), Row 3 (Red), Row 4 (Green).
The keycap in each specific row can exchange them. i.e Row 1 exchange with Row 1.

There is a keycaps profile from Signature Plastics do have same height in whole set. DSA profile keycaps, but very expensive.

Yes or no in the way most of them are same. Some so called mechanical kb like Logitech with "romer g"  switch doesn't feel like mechanical kb to me and of course they are not interchangeable to other key caps.

Besides of different switches, there are also different layout and keycaps profile. Eg: if you have an old steelseries 7g or 6g v2, they are using a chunky 2row "enter" which is not standard.

Not likely for customize mkb with RM300. Just reach some shop with demo unit and pickup one that you like the most. Special input signal needed for linux can be done by some software.

87 switches + some stabilizer + shipping is already about 300 d

Buy new board.

You can ask her back, "You can have many handbags so, why can't I have many MKB?". Just hope I don't see your name in the obituary after that