Questions about SOLR documents and some more

Question

Website: Classifieds website (users may put ads, search ads etc)

I plan to use SOLR for searching and then return results as ID nr:s only, and then use those ID nr:s

Answer 1

2- Should I use only one SOLR document, or multiple documents? Also, is document the same as a SOLR index?

3- Would it be better to Only use SOLR and skip MySQL knowing that I have alot of columns in each table? Personally I am much better at using MySQL than SOLR.

A document is "an instance" of solr index. Take into account that you can build only one solr index per solr Core. A core acts as an independent solr Server into the same solr insallation.

http://wiki.apache.org/solr/CoreAdmin

Yo can build one index merging some table contents and some other indexes to perform second level searches...

would you give more details about your architecture and data??