I have no idea what games will (not) work with the MK4.
So I'll stick to the current available stuff.
You can check if the games you have will work with the MK3 (you could post what games you have here and ask people over here if they will work).
NDSpatcher from |{ain is also an option (check the ndspatch list at
www.dualscene.net ).
However if you want all your games on one card, size may be a problem (GBAflash card are usually not that big).
And maybe the M3, G6 or something, but I have no idea on those.
And then you need a Passme (2) or Flashme (WIFIME WILL NOT WORK! IT ONLY MAKES YOU BOOT HOMEBREW! or well, with me anyway

, so I flashed my DS)
Also please check what firmware you have, then you know if you'll need a passme1 or 2