(sorry for my eng dude, I'm from Ukraine)

So, I make the full automation for every quality using circuit network and tested the most prices for upgrading Items and I can give feedback

My options:
"allow-multi-step" disabled > so I need to upgrade resources to higher quality
final cost are set to 2.5

most of items are very cheap for 1 > 2 upgrade, cuz my factories can make 12k/sec of upgrading resources, but I can't use more than 1500/sec with most items (only artillery shells and 3rd modules cost good)

upgrading for 2 > 3 are normal for price, because currently with my factory expanding I can make only 1600/sec 2nd quality upgrade resource

upgrading for 3 > 4 a lil expensive cuz a large factory can't create a big amount of 3rd quality resource, cost is normal only for regular resources

upgrading for 4 > 5 is useless when cost bigger than 150, it's worth only for upgrading something in a little amount such as turrets or buildings

So my suggestions:
1 > Make separated adjustment for every quality cost

2 > Make "tiers" for resources, like: ammo(tier 1) have own cost, science pack(tier 2) and buildings(tier 3) has another cost, tier 0 is regular adjustement

3 > Remove the cap of minimum 5 resources for upgrade, u can down cap 1res, and make that recipes every time upgrades only 1 item, I hate upgrading 2 electric drills xD (default options)
more about why I hate when recippe has bigger than 1 upgrading item - my automated upgrade factory contains 8 buildings, and sometime building receive only 1 upgrading item when recipe requires minimum 2 xD

4 > Separated cost adjustment specially for upgrade items

And yeah, I can help u with translation your mod to ru/ua lang, also can help with algorithms, tier lists, formulas, etc. not with coding, cuz I'm not fully understand LUA, I'm Java/C# programmer xD

you can contact me in discord: snoop1cattz69

Hey, thank you for your feedback!

1 > I added the options.

2 > This sounds quite complicated regarding compatibility with other mods. I would like to keep it generic with the current complexity system.

3 > I reduce the minimum to 0.1, use at your own risk (if crafting is too fast the quality upgrade might fail).

4> This is already an option: "Upgrade item upgrade cost scale".

The settings are also explained in more depth here: https://mods.factorio.com/mod/quality-processing/discussion/68d18d6091babbb95dbc7e97

3 > I reduce the minimum to 0.1, use at your own risk (if crafting is too fast the quality upgrade might fail).

I mean Item that will be upgraded, not time or upgrade resource :)

The number of items that are upgraded depends on the minimum time. For example, if from the settings the upgrade time would be 3s for a single item, but the minimum time is set to 5s, the system will produce a bulk recipe that upgrades 2 items in 6s. So, if you reduce the minimum upgrade time, more recipes will be for single items.