There are a few issues I noticed with the current progression system of storage upgrades.

First, I do not understand why emeralds are used for the highest tier storage upgrade instead of diamonds. Emeralds are extremely easy to get once you have a few villagers and can also be farmed infinitely. Diamonds require mining to obtain, and, unlike emeralds, are finite. I think it is obvious which one should be required for the max tier storage upgrade. Also, requiring a technically finite resource for the max tier storage upgrade would force players to assess whether the investment is worth it, or if realistically they would actually be fine with level 4 storage upgrades.

Second, though the materials used for the first three upgrades (iron, gold, and obsidian) are all technically renewable, obsidian is way harder to obtain in my opinion and deserves to craft a way better upgrade than level 1?? The only way to renewably farm obsidian is to either intentionally break nether portals behind you just as you travel through (such as with tnt) so it generates a new one when you enter again (which would be the tedious way of getting obsidian) or trading with piglins which requires a lot of gold for a small chance of a few obsidian. Iron, as of 1.18, can be found in MASSIVE amounts via the new iron veins. Just yesterday I got several stacks of raw iron blocks from over 7 nearby iron veins. Gold has no vein but can be obtained in large quantities from zombie pigman farms.

So in conclusion, I suggest the following progression:

1(I): copper (very common/copper veins)
2(II): iron (iron veins/iron farrms)
3(III): gold (zombie pigman farms)
4(IV): obsidian (piglin trading/very slow lava farms with manual mining)
5(V): diamond (finite/requires mining)
6(VI): netherite (very finite)

I guess you could have this be iron(I) gold(II) emerald(III) if you wanted to keep emeralds in here somewhere, but like I said, they can be obtained in MASSIVE amounts from villagers and would be best left out of this progression, hence why I replaced it with copper instead. Also I think a netherite upgrade that grants x64 storage would be cool and provide additional utility for those who wish to make this very expensive investment (two ingots). This could also provide incentive to go out and search for more netherite, becuase normally there is no reason to once you have full mending netherite armor and tools (unless you have the ice and fire mod becuase those sea serpents seem to always break my fully enchanted netherite armor somehow).

Also the void upgrade should require eye of enders or at least ender pearls