Is it possible to download ubuntu 16.04 for an i3 based machine which doesn't connect to the internet by first downloading to an amd based machine and then creating a bootable usb? (The download page detects the amd and starts to download the version for that, so I need to be able to choose one suitable for an i3 processor and get that one, I already have ubuntu on the amd machine).
AMD64 is just another name for the x86_64 CPU architecture. Points relevant to you:
On balance, 64bit is the clear winner these days.
Get that, ignore that it says AMD in the arch name. It's just a name.