SOG pot size

Here theres a nice article about it https://www.royalqueenseeds.com/blog-how-many-plants-to-grow-per-square-meter-n774

3-7 Liter !

Dutch buckets, rest depends on type of weed, auto or photo, if photo clones or seeds... Generally it's around 10 liters If you want to save and optimise space, it's only that way. All the Best !

6 inch pot is pretty standard for SOG. It allows for 4 pots per sq/ft and makes it easily scalable for different grow room sizes, it's symmetrical, etc. Bottom line for you should be what can you acquire. Getting pots online from Amazon or Walmart can be convenient, but if you find a local store that has the sizes you need on a seasonal basis, you may want to go with them for convenience and availability. Especially because SOG requires more soil, amendments, pots, germinating space, etc. so having a local store that buys the same stuff year to year will make it easier in the long run in my opinion.

seek for examples in here : growdiaries.com/explore

That depends how big your tent is. I'd aim for 1-3gal wall to wall But if the space is bigger could increase pot size. Good Luck!