I'm going to work backwards through the questions: (1) Yes, you can upgrade the fusion drive to an SSD. However, you will be unable to use the OWC Aura Pro X2 SSD due to the interface (connection to the logic board) it requires (PCIe). Your iMac supports the SATA (6GB/s) interface, so you would have to use something like OWC Mercury Electra (6G) . (2) I believe the current iMac you have is a powerful enough machine to be able to handle the work load you are going to throw at it. Assuming you become a competent user with relative ease, the specs on the machine would likely be able to support you for the next 5-10 years depending on the amount of storage you buy when you upgrade. (3) I think your iPad or iMac question comes down to your seriousness in your professional pursuits and how are you going to use the machines. The iMac is more powerful processing power; ability to edit video and audio at the same time (1) The iPad will be able to support a process, like editing video, you just won't be able to do...
What about disconnecting the battery?
Isn’t there also a Samsung Certification?