Need Solr Whiz for Early-Stage Guidance

I need a suggestion on how to proceed with a new project from someone who understands the architecture and capabilties of Solr within Drupal.

I'm hoping to put together a basic "search project" system where people initiate new searches as nodes and collect "items" from an external, non-Drupal Solr index populated with tens of millions of records. The result set needs to be browsable and faceted just like the integrated result set would be, with drill-down to smaller row sets and such. Then a user would need the ability to click a link much like the Drupal "flag" module where he could rapidly "bookmark" many of the results from the set to associate them with the currently-open project. Finally, those items would somehow need to be imported from the external Solr or MySQL as nodes within that project, properly mapped with Flags, Collection, Node Associations or some other such method/mod. Oh, and finally, I must have all advanced search syntax available, not just the DisMax handler.

I need suggestions on how to proceed with the Solr solution. I've thought of the following options so far:

1) Import millions of nodes and use ApacheSolr Search Integration out of the box. It actually kinda worked, but I could get into heaps of trouble if I continue?

2) Write my own everything and frame it into Drupal, wrestling with how to call methods from outside over services or through the backend, or possible MySQL triggers, etc.

3) Use ApacheSolr SI but don't use the default XML configs, possibly add ApacheSolr Ajax module or views3 and Solr Views, or Nutch, or something else? Seems awfully hacky at this early stage and I could encounter severe road blocks.

4) Turn to the community for something brilliant I would have never realized and continue to be amazed at how amazing Drupal can be if you're willing to pay your dues...