Ok...where is it that you live, what is the USDA zone? Have you ever used a greenhouse? Will it be heated and if so how?
I had a polytunnel greenhouse until this last winter when we got tons of snow. Completely collapsed the greenhouse. Had a couple of mild winters so got lulled into complacency, sigh. We are doing a better and more permanent greenhouse now. I have lots of perennials and most seem to have made the winter being squished under a ton of snow and expensive plastic cover.
I don't do pots, the greenhouse would have to be heated and plants constantly being transplanted up...I use the soil the greenhouse is built over. Just like a garden out of doors. I have used lots of decomposed compost and keep the beds mulched with fresh decomposed compost. I've got raised beds (without borders) walks and I can grow a heck of a lot. I use a few pots for tomatoes and starts but I can keep blueberry shrubs, bosenberry vines, kiwi vines, asparagus, strawberries, herbs alive season to season. I would simply double dig 3' wide rows/penninsulas with deep trenches to allow for better drainage. Or even 6' wide beds with a narrow walkway on both sides A main path that supports my beloved cart width and tiny little foot paths between the big fluffy penninsulas/sections. Growing stuff in pots wastes so much resources and labor. My opinion. Do you have snow? You do know that we aren't in global warming, yes? Grins!! More like global cooling...
And do you really want such a small greenhouse? A tad bigger wouldn't cost much more!