Agree about the disparity in sizes, its frustrating having trained my neighbours to "recycle", i.e , donate their emptied- from- the- garden- centre pots. If only they would all shop at the same place. I also visit the nearest place , where one can 'cadge' pots complete with their trays, all of which are "one-trip", and go to the tip because the plastic materials are different blends of recycled material and will only be recycled once.
For storage, they are (sometimes!)washed and sorted into sizes and then hung in tough plastic sacks (Dustbin liners 37"x18") on cup hooks at the dark north end of the shed (Outside), away from sight and sunshine. Six sacks hold the range of sizes upto 10", then any big ones stack upside down and give perfect shelter to the snails.