That should help you understand where you can look for performance optimizations. The caveat here is that some of the Commerce objects may be dependent on the ASP intrinsic objects so you'll need to design your VB component with that in mind. No, there's really no reason to do this that I'm aware of, Search and Index don't use each others' services. The question is, which one more closely fit's your needs. Search can do Exchange PF's, ODBC datasources, file crawl, and http crawl, while index only does a file crawl.
Index does automatically update itself when new content is added however.
Search needs to be scheduled for a refresh. Not that I am aware of. In fact, it should be quite similar to how you access the objects in ASP script, with the added step of using the ScriptingContext collection or the ObjectContext to access ASP's application object. Thanks for the heads up on the BO4.5 install. Content Deployment in Site Server can be used to automate the staging, especially if there are many web servers you need to push to.