Very nice review and thanks - definitely helped!

1) I did not bother putting the metal retaining clip back in again. It was nearly impossible and to be honest, found it to be useful - as many others here did.

2) I used a cheap SSD that works well - Kingston 240GB A400 SSD 2.5'' SATA 7MM 2.5-Inch SA400S37/240G . $30 and made a HUGE difference in performance.

The easiest way I found was to connect it via an external USB caddie, wipe, clean install (Mojave), and boot from that. Afterwards I did the disk replacement.