I have a game called WITCH, and I'm intending to make some "supplemental spells/adventures" for each of the eight witch types. There'd be three spells/adventures in each pack.

Ideally, I'd like to have all the adventures be available on a single project page—Witch Adventures, we can call them collectively for now—and have each pack available on that page for its own price. So if each pack is $3, you could buy them all for $24, is what I'd like to be the case. Since you generally play as one witch type, I imagine people would want to just buy the pack that corresponds with the witch type they're playing as.

However: "The minimum price for a file should be greater than the minimum price for the entire project." I can't sell all of them individually on the same project page and have the buy-them-all price be $24.

How would you go about doing this in the cleanest way? Just make 8 project pages, one for each pack?

The only way to do this is through "DLC," creating a project for each deck you want to sell and activating the condition that they must already own the base project to purchase that DLC.

The downside is that Itch doesn't have a shopping cart, and if someone wants to buy your eight decks, they'll have to make eight separate purchases, resulting in eight transaction fees.

Itch doesn't allow you to selectively purchase files within the same project. Instead, it has a Tier system, designed so that people "donate" a higher amount than the suggested price or the base purchase price and receive rewards based on that extra amount. Note that in the per-file pricing system, the condition for accessing that file is having made a purchase with a total value equal to or greater than the file's price.

If you have eight files priced at $3 each, to access all eight files, a single purchase of $3 or more is sufficient.

For what you're proposing, the only way I can think of is for you to have 8 separate projects/pages.

Make all 8 pages into a bundle priced $21-$24 so that if any one wants all of them, it is one purchase.

Individually priced files are not what they seem to be. In general, they are not a good option for anything. The only clean option they give, is rewarding buyers on a 0 cost pay what you want game. Other than that they are very inflexible. Want to increase price later? You can't. The individual part means only that the buying price of a project is compared to the "individual" price of the file - at the time of download. This practically means, that the buyer did not buy anything. And if you do things like raising the minimum price above the individual price or increase the indiviudal price, you screw over all buyers that "purchased" it at that price. It is a horrible pricing option for a store. (Did I mention that you cannot increase your payment tier? Pay 5 and pay 5 again and your tier is still 5 and not 10, but now you have the game twice in your library. So it is an utterly useless and misleading option to offer a game for 5 and have an individual priced dlc file at 10.)

There is no conditional projects as far as I know. You can have conditional sales. That is, offer a project for reduced price, if a specific project is owned by the buyer.

The cleanest way of having dlc is seperate projects. And if you want to avoid clutter, you can have those projects only be linked by the main page, instead of trying to have them appear as regular projects. You can bundle projects and bundles can have a separate discount.