As other professionals has mentioned, you can not and you should not use the underlying SOLR search engine for Content Manager/Broker Database. If you want to use the broker data you try to explore the OData Service (aka Content Delivery Service).
To use SOLR (or in fact any search engine like Endecca, MS-FAST, Google Mini etc. ) as a search engine for your website and integrate it with SDL Tridion, a detailed generic approach along with High level Architecture has been defined here (keeping in mind the FAQ for this site; the link shared is of my personal blog)
As you are asking for best practice, please consider following scenarios (I am assuming you must have done this much research)
Are you planning to have a Single Core or Multi-Core SOLR - If it is a multi-core SOLR, then keep your Blueprinting in line with that
If you are planning to index static components which are embedded in pages as well in SOLR (Which I really don't see a reason unless you are planning to use SOLR itself as a Crawler), then for such components use the Event System to index them in SOLR
Also for SOLR related queries I would recommend posting separate questions going forward in respective communities meant for SOLR, but to close the loop, below are the answers:
1) Regarding SOLR integration with Crawler, you have veriety of crawlers available like Tika and similar which provide integration with much ease - Explore/Research further on SOLR communities
2) If you want to use SOLR as a Web Crawler, you can do so depending on your business requirements and architecture where you are supposed to index all the components with all their fields into SOLR. This approach comes with a disadvantage when you have to deals with
trillions of data and with an advantage that from your website you need not to connect with Tridion at all unless for internal Link resolution which will enhance your performance
3) Also, keep in mind that if you are planning to use multi-core SOLR, do not use SolrNet API instead take help of Third Party APIs like StructureMap or Castle Windsor meant for it.