Drain holes are under the battery. I've had this on my a6 as well as the pollen filter housing cracking. Both causing water into the footwells. Needless to say a new ccm is on my list of jobs.
Truthfully we've not got many q8 owners yet. I suppose my logic would be the q7 is an older design abd therefore more likely to have had any issues ironed out. But I guess it depends on whst size of car you need as the q8 is larger.
Unfortunately you would but the update should be free. However if you chose to update the sat nav then this will cost you. Also bare in mind Audi will want to probably charge you a £50 diagnostic fee too.
If you've bought this within 30 days from a dealer then you have the right for them to sort it as you're entitled to a full refund within 30 days of sale.
It's so annoying as these seem to break regularly on vag cars.
My first advice would be to see if it needs an update to the infotainment system. This isn't the same as sat nav update. Or a diagnostic check. Alternatively you could try and do the system reset which should be in the owners manual.