I don’t have any SSD experience.
I have installed (I think it was opensuse 13.2) on an external drive, to boot either on UEFI or non-UEFI.
Partitioning: You will need an EFI partition, formatted to FAT. I suggest 128M, though 50M might be big enough. If using Legacy partitioning, then give that partition a type code of “ef”. I suggest GPT partitioning, and the partitioner that you use should be able to set the partition type for EFI. Or set the type code to “EF00” with “gdisk” (for GPT partitoning).
I suggest also a bios-boot partition (sometimes called “bios-grub”). This assumes that you are using GPT partitioning. It is possible to use Legacy partitioning, though the installer might complain. With GPT partitioning, you need a bios-boot partition to install grub into the MBR. I usually put the bios-boot partition in sectors 34-2047, which is space not normally used for other partitions.
Then use whatever you want for other partitions.
I suggest that you first install on a UEFI box. For that install, mount the EFI partition at “/boot/efi”. If you already have opensuse installed on that box, this might mess up booting to your already installed system, though that is fixable).
After you have completed the install, get to a root command line (or root konsole or whatever). Go to the directory “/boot/efi/EFI/Boot”. Delete any files there. Then copy the content of “/boot/efi/EFI/opensuse” to that directory (to “/boot/efi/EFI/Boot”. If the copied files include “shim.efi”, then rename that as “bootx64.efi”. Otherwise rename “grubx64.efi” to “bootx64.efi”. In the latter case, you will have to turn off secure-boot to boot this external drive.
Next: If you did not already have opensuse installed, then delete the boot entry for this, using “efibootmgr” (check the man pages and google for examples). If you did already have opensuse installed, then you can use “efibootmgr” to fix booting back to the system installed on your internal hard drive. Again, check the man pages and google for examples.
I recommend rebooting after these changes, to see if it works. On many UEFI systems, you can hit F12 during boot to get a boot menu and select your external drive.
Once this is working, boot into the system and use Yast Bootloader to switch to “grub2” (instead of “grub2-efi”). Then click the button for “Boot Loader Installation Details” (toward the bottom left, after the switch to “grub2”). That should give the disk order. Make sure that your external drive is first in disk order. Click OK on the disk order settings. Then check the box “Boot from Master Boot Record” and uncheck the box “write generic code to MBR”. Click OK (and then probably “Finish” on the next screen). Your system should now be bootable on non-UEFI systems, provided that you can set the BIOS to boot the external drive.