Dual booting install USB (mixing gpt/mbr)

In my odd few bits of family and friends tech support I've been recently installing Windows 8.1 from USB. However some are uefi and some old bios setups. I've just got a present from someone of a 16GB USB stick and now I'm thinking of three partitions:

1. 3.5GB GPT Partition
2. 3.5GB MBR Partition
3. (the rest GB) Partition

The first two contain Windows 8.1 in the two different USB install types and the third is a data partition containing drivers etc.

Would this work easily? Would a uefi boot straight from partition 1, an mbr partition not see partition 1 and use partition 2 etc? Been getting tired of USB rewrites etc! In fact I'd even like a little partition for a Linux diagnostic for detecting hardware faults if possible, tips on that?

Typically you can not put several installations of Windows onto one USB.

I would suggest looking into Yumi Multiboot USB Creator. It sounds like what your looking for.

Assuming you have an .iso of what ever, you can pretty much add it. Like on one of my USB's: I have tails, Live XP OS, debian install, falcon repair, Acronis Repair, some Linux multi Repair.. etc.