To calculate the length of a frame for any given settings you can download the spreadsheet linked to from here: DW1000 Power Calculator not working
If you go to the TWR Exchange tab and set the packet settings/length on the left it will calculate the frame length.
Minimum frame size if 3 bytes. Maximum is 127 bytes sticking to the IEEE standard or 1023 using the decawave only settings.
The frame overhead is dominated by the preamble length, there are other overheads but that is by far the largest component.