However, are the presets and parameters assigned midi program change numbers and cc's by default?
Yes. The MIDI maps allow you to change these, but you do not have to.
Is pre/post functionality midi switchable?
If you are in pre/post mode, whether you use pre or post is set on a preset by preset basis, and is not otherwise selectable. You presumably could save a PRE and a POST copy of a given preset and select it with MIDI Program Change.
Tempo is saved with the preset but you can have midi clock supply tempo which I will have from another device. Can you temporarily override the midi clock tempo with tap tempo?
No – you have to choose one or the other. This is because you might set up a tempo with the TAP, and then the MIDIclock might change slightly, and set it to something else. Best you stick to one or the other.
Can you setup the parameters assigned to the hotknob from the control app? I like the idea of the app instead of diving through partial menus on the device.
Is there a limit in the H9 app for the number of presets you can save and transfer to the pedal?
The pedal will only hold 100 presets. There presumably is a limit on the App (don't know) but you will probably lose track of which preset is which before you hit it.