You can use any and all of the USB MIDI interfaces connected (and supported) including the ones that are part of the audio interface. So you could plug in a combined audio and MIDI interface and use both the audio and MIDI of that device. You could plug in extra MIDI interfaces and use them. You cannot (easily or efficiently) use more than one audio interface. You cannot hot swap audio interfaces. It has to be connected at boot and configured correctly in webconf.
If you have a USB audio interface that is not listed in webconf then you can choose Generic USB Devce which works with most “Class Compliant” USB Audio devices. (Class Compliant means the interface uses a standard audio over USB standard. Some devices may use proprietary interface requiring drivers which may not be available for Linux.) USB MIDI tends to work. Again class compliant devices should just work. They don’t need any configuration although there is the ability to configure some filtering in webconf - but that is generally for more complex workflows.
The Tascam may work - there are mixed reports. One such report said it started to work after a while of being plugged in. If this happens then it may prove unreliable because Zynthian depends on the soundcard being available from early in the boot process. Please try it and let us know of your success. The other cards you mention should work but again, let us know your success.
Good luck!
[Edit] Steinberg is in the list on webconf. If it is in the list then someone has tested it and given us configuration so it should work.