Overlapping Canvases will ever cause problems, as canvases are not regular gadgets, they are not meant to be put above others and have other gadgets put above them.
If you need to redraw them its up to you, you will just have to react to the GadgetRepaint event.
Performance is around the regular max2d in windowed mode, fullscreen will always be faster.
HTMLView reads from files but those files can be created as TStream as well and read from there. so an own THTML object or the like where you change parts of it and that updates a TStream source should work without problems.
If you need to redraw them its up to you, you will just have to react to the GadgetRepaint event.
Performance is around the regular max2d in windowed mode, fullscreen will always be faster.
HTMLView reads from files but those files can be created as TStream as well and read from there. so an own THTML object or the like where you change parts of it and that updates a TStream source should work without problems.