OK, first of all if those two units are as I suspect just apl video in then the computer display on the screen will be crap. What you really need to get is a proper VGA capable screen. Unfortunately at the moment there is no main brand name that does them.
Have a look a linitx.com for the screens they do.
There have already been a few E39 installs done, so I would recommend you do a quick search for the related threads and have a good read through those.
It wopuld also worht looking up the user Sama as he has an E39 and is also London based so might be able to give you loads of advice.
Oh and IBUS is your friend as far as data from the car is concerned, not sure how much of the OBC data is available, but I have kept mine (E36) as I don't have IBUS.