Cross-posted with you there.

Just to be clear about your first question, the answer is yes Windows will boot normally if there's nothing in the removable drive (usb in your case). It looks at the devices in the order you specify until it finds one it can boot from. If there's nothing bootable in the first device (either there's nothing in the drive, or there is but it's not something that's bootable) then it will ignore it and try the next device in the list. If it reaches your hard drive without finding anything else to boot it will boot Windows from that as normal (or if you have several systems installed it will offer you the list of them as normal).

And to reiterate, the Ubuntu installer should recognise your installed Windows system and offer you the option to install Ubuntu alongside Windows as you want. (I can't remember if that's the default option; I would imagine it is, but the choice is clear anyway)


Mick