XI and Basis

What are all the Points needs to be addressed for the Basis team, when 3 R/3 Systems are going to be connected to the XI system for the B2B Document Exchange Process?

I have few points

1) Installing B2B Adapter 2) Installing Certificates(Internal and external)

3) Scalability 4) Fall Off

5) Other security Issues

Let me know should i need to add anything more in my list.