Was surprised to find that the Geeetech doesn't have the same size spool holder as my Creality (why, oh why, can't manufacturers decide on a universal spool hole size and stick with it?) and had to make a bushing to allow Inland and Zyltech spools to sit comfortably on the spool holder.
The large washer is optional and only needed if you have a particularly skinny spool.

Geeetech A10

No

No

0.12mm layer height

15-20% should be more than enough