Love your mod so far, really really helpful. I know its still young and so has much room for improvement, but even now I'm finding it very convenient.

Ok, here's my UX suggestions:

1. Have a separate section at the top of the UI where you move all items that currently have a logistic request set on them, makes updating existing amounts a lot less painful in modpacks with large item lists.
   Additionally, to keep the item from jumping back into the list immediately when you clear a request, I'd recommend making it so adding a request for an item immediately moves it to this top section, but clearing the request for an item doesn't move it back into its category until you close and reopen the UI. That way misclicks (don't force the player to sift through the item list to find it again (which will happen a lot early on as people learn the controls).

2. Add a second level of collapsing/expanding items, this one grouping items by their upgrade/downgrade groups (so items that can replace each other using an upgrade planner). This way it automatically works for items added from mods. Would make navigating easier

3. Add support for Control+F similar to most other native factory UIs (if this is possible).

4. Instead of making your mod open by toolbar button, do what even-distribution does for its settings, and add a button to the side of the inventory screen (you can see a picture of this on mod portal page for even-distribtion). I think this make sense since your mod only is used when an inventory window (or spidertron inventory window) is being used.
   Alternatively/additionally, make the request helper window automatically close when the currently opened inventory screen is closed (if possible) or make the help window close when the user presses the escape key (if possible).

5. In help text when hovering over an item icon in your window, the text is not intuitive to read. It does explain the behavior correctly, it just takes a lot more mental energy to parse it than I think it needs to.
   Here's my recommended rewrite of the help text to make it clearer at a glance (also updated to use the same language factorio uses for the Request Amount and Max amount):

Alt + Left Click - ↑ Request Amount
Ctrl + Left Click = ↑ Max Amount
Left Click = ↑ Both
Shift + (Any of the above) = ↓ Request/Max/Both instead of ↑
Right Click = Clear Request

Hope this was useful! Thanks for the amazing mod!