I have been doing the old skool way of planting ( rows and lines)
I've mixed Mels Mix and added it on top of my existing soil. Should I remove everything and add a liner at the bottom?
That's a really interesting question.
What can you tell us about your old skool soil?
If it is all good, and I think few soils are realistically bad, the worms will mix the soil and Mel's and make some thing better out of both. Synergy.
I wouldn't line it. Plants can grow their roots deeper into the old school soil, while still reaping the benefit of the looser layer of soil filling the bed.