Hi Ian,
ad (1): There shouldn't be any compatibility issues with the Joomla itself, however some components may interfere with JoomSEF functionality.
ad (2): I'm not sure if that would work. Maybe if you turn the JoomSEF's MetaBot off, the SEF patch could work normally, but the behaviour is quite unpredictable, as I don't know how the SEF patch works.
I think you should first try the free version of JoomSEF to see if it suits your needs.
Regards,
David