The VE images are specific to a hypervisor, so you must know what they use so you can provide the correct one.
Big cloud providers, like Amazon, have their own F5 image, that is available in their system.
Here is the link to latest files:
https://downloads.f5.com/esd/ecc.sv?sw=BIG-IP&pro=big-ip_v13.x&ver=13.1.0&container=13.1.0.2_Virtual-Edition
The description says the hypervisor.
In relation to the type of images, see this solution:
https://support.f5.com/csp/article/K14946
In relation to disks, yes the "ALL" will include 2 disks.
However, I expect the other types to have only one, but I not sure if that is the case.