We plan to add more tooltips and a tutorial, especially for the inventory screen.
The affinities (type of damage) are our new feature, and the details about what the icon positions mean is currently only in the devlog. Top left is what you are strong with. Top right is what you are weak to. Below the name is what you have armor against. Items only show the strong/weak affinities and do not have a separate armor value. We'll need to think about updating the icon tooltips with more details, though we are trying to design with cross-platform in mind and the current tooltips already don't work for keyboard/controller, so are under review for a better way to convey the info.
The inventory has a lot and we want to improve its UI. For now we just have the Help button with text descriptions of how things work in there, but we plan to add a tutorial to point out the controls, as well as update the Help screen to include images. We plan to add a few shortcuts for moving items, such as clicking on the tab of a Slime who's bag is already selected moves a selected item to the open slot (Edit: this will be in the next update), but the main idea right now is to use the filters to control which items are visible, and then use the bulk transfer options to move them into the individual bags. The left-most of the bottom buttons controls how many items are moved by the 2 bulk transfer arrows, so you don't need to choose between 1 or all, but have several options, including 1 at a time but using the transfer button, instead of scrolling to the last slot. The belt slots need to be managed one by one, but they have limited slots and generally should not need regular adjusting, since they are filled from the personal bags.
The belts do take up a lot of space, and we'd like to reduce that, but we also want each to always be visible so you know what you will have going into the next combat, and with the current sizing that was the best layout we came up with. We will be looking at this and seeing about better use of the space. Depending on how things go we may add some tabs so you can see other info in that area for each Slime. We are trying to keep things from getting too complex, so don't want to add too much extra text and details, but just enough for the player to feel like they know what to do.
Currently, the order of items does not matter. We have been debating various ideas about order mattering, such as items closer to the top being more likely to be picked, but don't want to force the player to spend extra time sorting things if they don't want to. Also, once we implement auto-sorting, if you prefer to have your bag sorted by item type, that would mean the type sorted first would always be favored, and would not play as well for everyone.
Thanks for playing, and the feedback! UI is an important part of making this fun, so hearing how different people view it helps us make a better system. We appreciate honest feedback!