UEFI, Delta Auto Boot, FS Number

Hello,

I'm trying to have my Lattepanda Delta autoboot with the application of power. I'm currently following this tutorial. 

GitHub Tutorial 

I have two questions. One being, the tutorial tells me to enter FSX in the UEFI, X being the number of the USB flash drive I have plugged into the USB port. How do I know which FS number this is. Documentation online about this question seems strangely sparse. 

Second question, I was trying to format my USB drive to Fat32 as instructed, but it only gave me the option of exFat. Will this suffice?

I got this link from another forum post on this site found here. https://www.lattepanda.com/forum/topic/314325

These questions however are not addressed in this link.

Thanks