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

I would really like to know: Is there any fundamental difference in developing a multi-network site as opposed to a normal wordpress site?

More Specifically:

1. Is the wordpress plugin development process the same?
2. Is theming the same? Can I use common AND separate stylesheets?
3. Will my old WP queries continue to work the same across the site network?
4. Can I expect popular wordpress plugins for taxonomies, custom fields and custom posts to work seamlessly across the network?
5. Can I create custom post types that are unique to each network?

I am completely new to multisite but am totally game with the single wordpress install. Would really appreciate guidance from this community.

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