Is there any fundamental difference in developing a wordpress multi-network site?

Essentially, a WordPress network is number of almost totally unique sites which answers most of your questions: you can proceed as you normally would.

The network allows you to share the database and file system, but each site is unique and the only main feature shared between each network site is the user system.

To answer each question though:

1. Yes — however, you can create network-specific plugins that do some things at the network level, rather than simply network activating a plugin (a new instance for each site)
2. Yes
3. Yes
4. Yes
5. Yes — each post type is necessarily unique to its site