In relation to question #2, oak has a greated density than typically used tonewoods and greater thickening and lignification (the process of laying down lignin in the fibres, vessels and other cells that makes wood "woody" as opposed to herbaceous plants). This makes it inherently stiffer than typical tonewoods with less freedom to vibrate, hence the muffled sound.

Having said that, it is perfectly possible to use hardwoods (as opposed to the coniferous "softwoods" like spruce, pine and cedar that are typically used as tonewoods) for the soundboard and there are many excellent-sounding instruments that use, for example, mahogany as a tonewood. In this case, top thickness will need to be reduced and bracing redesigned to allow the necessary flexibility and vibration of the top.

Hope this helps a bit.

Keep up the good work!

moo