Asset icons can be added via plugins now (see FClassIconFinder::RegisterIconSource/UnregisterIconSource); I filed an issue for that and went ahead and added the icons to the main editor style as a stop-gap, but haven’t moved them into the plugin yet.
One-line tooltips can be in the plugin, but rich tool tip documentation is still currently limited to the Engine/Documentation/Source/Shared folder. I’ve mentioned that before but can’t find a JIRA on it, so I’ll file one. I think plugins can also define a docs URL overall, that might show up in the plugin wizard, not 100% sure?
RE: the scroll bar showing up, I’m not seeing that , are you adding a bunch of options or just one? I could see there being a max height before it throws in the scroll bar, and in general the look/feel of the filter menu isn’t ideal.
Cheers,