1. No, vBulletin software is simply software. You need a webhost with PHP & MySQL capability.
2. Depends on your level of customization. Can take a few hours to a few days for full settings. You'll also need to be fully aware of forum infrastructure & knowledge terms otherwise you'll be doing a lot of catch-up reading.
3. You need technical knowledge for some areas. You need to have your MySQL database connection info handy, standard text editor, and you need administrative interface common knowledge.
4. Skins aren't hard to put on. But they are hard to customize. Most people purchase their own. In order to truly customize a skin, you'll need HTML skills as well.
Any other
vB related concerns are addressed in the FAQ @ vBulletin.com
vBulletin® - Frequently Asked Questions - Sales