The Z value is the relative distance between the print nozzle and the print surface, always keep that in mind and it is much easier to decipher what is going on!
As for the z max value, it will vary a bit depending on your exact assembly and can even be slightly increased if desired by adding washers to the top of the bolt that triggers the z endstop to cause it to trigger later. However, you run the risk of having not enough space down below and the bolts for the heated bed may hit the base plate! 255mm is a safe value, but 260mm could probably be achieved if it is absolutely necessary for whatever reason!
Thanks for the Z axis information. I have that all working now.
Now I'm having issues with Windows 10 seeing the Smoothieboard over the USB connection. After a Google search I'm finding out there are issues affecting COM port serial communication and it causing the serial driver to randomly stall for long periods of time. I'm getting "reset send buffer block" errors in Repetier.
Oh haha didn't even see that question! In repetier settings all you really have to set up is the printer size (200 x 200 x 255 or whatever your z is). Everything else can more or less be left default. You can change the default temp settings for the hotend and heated bed which is handy but other than that there isn't much that needs changing.
And yeah windows 10 is a bit of an issue, I believe you just have to find the right driver package but I unfortunately have no idea where that would be. But glad sd printing is working at least!