Replacing SATA I with SATA III? Replacing optical drive with an SSD?

Hi there, I have a few questions about the optical drive in my Inspiron 5558 :)

1. I want to replace the SATA I Interface of the optical drive with SATA III. Is this even possible? Is the SATA I part of the main board & can't be replaced?

2. My old 2TB had some bad sectors & died. I got a Evo 860 to replace that. I don't want to deal with HDD anymore. But is it worth it to pair a SSD with the SATA I of the optical drive? I'd love some suggestions on (dirt-)cheap 1TB SSD.

Thank you for your answers!