[Mythotical]

1) Templates are handled in the database, therefore you could integrate your site style with ease. Now when doing non vB pages, there is a tutorial that explains how to include specific features of vB to your non vB page especially the style but it might require you to edit the php file a bit.

2) Queries can be kept to a minimum if you only limit queries to where they are needed or pages they are needed on. With the style, it queries for the templates, each template, style, etc. Maybe 5 queries, might be less, can't remember exactly.

2a & b) Query count remains the same for members, guest viewing is lower count query.

3) No, this is warranted, you can find many tutorials here under articles to help you do this smoothly. There is also a paid request forum so you can hire someone to help you out.

HTH's
Steve