That's not too bad actually, the harnesses and connectors are all there and not 'hacked' off as sometimes can be the case. I think you might need the metal frame which holds the AC panel and the ASC/PDC bit in place properly, then everything will 'fit' correctly there. As you can see from my pic, the AC panel is uppermost, then the PDC/ASC panel and underneath that is the cupholders.
As for which audio units you go for, it looks like the harness for the radio cassette. I'm not sure if the harness is the same for the MID display panel, so if you want that setup along with a CD player just above (this setup will have split pieces) you might have to get extra harnesses and/or have the right clocks in the instrument cluster as well as coding to do.
Nip to bmw5.co.uk, as there's a few very knowledgeable guys who've done transplants etc with part numbers etc needed. If you post up a pic of your instrument cluster, they'll be able to tell you what bits will be needed etc.