I expect that support for most of the USB will be available on iOS 13 compatible iPads; however Apple is unlikely to provide hardware. You’ll be dependent on third party manufacturers for that. In most cases, a Lightning to USB hub should work. I doubt that anyone is going to make a multi-port Lightning hub. Mouse support is an accessibility feature. What this means is the mouse becomes a way to control a virtual finger in the touch environment. It will not work the same as the mouse you are used to. That’s not to say some people won’t find it useful, just that you should not expect to be able to select and move text, files, etc. differently just because there is a mouse. You’ll have the same gestures.