When i got my last hardware, one challenge was UEFI booting, iirc. After dealing with it, i sort of lost track of what was happening in that arena. However, i don't want to get involved with that again.
Motherboard firmware could be switched to the legacy BIOS/MBR mode, so you do not have to use UEFI if you do not want to.
But I do not see any reason to do so: UEFI just works fine nowadays.
In UEFI world, PC has a special small fat32-formatted partition with ".efi" file: it is an application written for UEFI. Motherboard's firmware (we call it BIOS, but technically it should be called UEFI) runs this application and it loads OS.
In Linux, GRUB provides this efi app.
If your harddrive is larger than ~4terabytes, you would need to use GPT instead of MBR, and I believe you would need UEFI to boot from it.
I'm sort of thinking about getting a Dell Inspiron but maybe i should buy from a linux vendor instead, such as 76? Presumably at least in that case at least i wouldn't have to worry about the bios.
Otherwise you would need to check carefully that all hardware is supported by Linux.
Not all devices have Linux drivers, unfortunately.
I certainly would want to get something which supported 2 or 3 internal disks, but i would also like to get something that could be booted from an external usb drive. Does that make sense?
Many motherboards have three SATA III ports. If you need something very fast you may also use nvme.
Almost all motherboards produced in the last 13 years can boot from external USB.
Would it make sense to look for something where all usb ports are usb 3.0? I've never used usb 3.0 at home, so i'm kind of unclued.
USB 3 is much faster and backward compatible with USB 2.0.
You do need this speed for mouse and keyboard, but it could be useful for pendrive.
All modern motherboards have 3.0. Even if some ports are 2.0, use them for keyboard/mouse.
In most cases 3.0 ports are blue, 2.0 are black.
In a way, i'd like to have something with 2 ethernet ports on the motherboard, although i've found that usb-to-ethernet is adequate for my purposes.
It is an uncommon requirement) Why?
Are you building a router or something with channel bonding