WML, SGD on Zebra printers ZT400, ZT600

Hi All,
I'm trying to create simplest as possible print station on ZT400, ZT600 by WML mechanism.
I stuck on few issues.
First, I know how to read and select stored template (ZPL file - *.ZPL) by SGD command  usb.host.template_list,
but I don't know how to print this selected file.

Second, I don't know how to use these SGD commands

usb.host.fn_field_data

usb.host.fn_last_field


Third, I saw that on ZT600 by WML, text is very small, how can I set bigger font.

I tried <big></big> from WML standard but it doesn't work.

kind regards
Adam