Start with the older machine. If it's 64-bit, then you can later make a uefi-compatible iso to use on the other machine. You would just need to use the beta version of refractasnapshot that has support for uefi and install the grub-efi-amd64 package on the older machine.
Add the word, toram, to the boot command. It goes on the linux line in a grub menu and on the append line in an isolinux menu. (grub menu only gets used with uefi, so you won't see it in your first snapshots.) If you're booting from a CD, putting it all in ram makes a huge difference in speed. If you're running from a usb stick, it's not such a big advantage. Note that with usb, toram will load the entire first partition, and that needs to be less than the total ram on the machine. If you transfer the isohybrid image directly to the usb stick using either the dd or cat command, the first partition will be the same size as the iso file.
However you configure your installation, add or remove whatever apps you want, the snapshot will copy those changes. That's the whole point - you get to make a live system that has what you want in it. Less software means smaller image, shorter times creating and transferring the image, and maybe faster boot times.
You can probably get away without any swap, but the usual recommendation is that there are a few things that expect it to be there. What I've seen is that even with enough memory, a little bit of swap gets used sometimes, maybe around 50mb.
Read the config file. It's the best documentation for the program. Look over the excludes file and add or remove items as needed.