Advanced Schema Design Question For Experts. Please Help. Thanks

QUESTIONs:
What schema is the best for high speed search for a classified web application?

Is our schema design looks OK? It is a STAR schema and will be used for OLTP type app. Is this OK? or Are we missing something?
Please let me know if you need more diagramatic description. 

BACKGROUND:
Our group is making a classified website (like classified.yahoo.com) where people can place online ad to sell items.
like cars, computers, electronics etc. Users will fill out webform for each category(car or computers) with all
attributes of the item forsell to post an add.



Main 3 operations the web users will perform:
Quick Searching(most frequent): category=car, subcategory=sedan, country=USA city=LosAngeles Zip=empty
 

Advanced Search(less frequent): 

  User can include all fieldsattributes or then can user a subset to query to do advanced search like :


   category=car, subcategory=sedan, country=USA, city=Los Angeles, Year= in(00, 03), transmission=Auto, engine=V6, Maker=Honda, Model=Accord, color=Red and Price < 10000


   category=car, subcategory=SUV, country=USA, city=NY, Year= in(99, 00, 03), transmission=Auto, Maker=Toyota, and Price between 11000 and 14500




 Insert(least frequent): By filling out web form. For Car, the form will have different dimensionsattributes (year, make, model, transmission, mileage, color, price etc)



Current Schema design:
Set of core dimensionlookup tables: stores corecommon attributes for lookups eg. status={open, new, expired}, country={USA, Canada, India,...}

One custom Lookup table: for all custom attribute lookup: transmission{auto, manual}, engine type{V4, V6} for car, processor{PII, PIII, PIV), RAM(512MB, 1GB, 2GB} for Computer & so



3 Fact Tables:
Main factPivot table that stores all sell common attributes eg. price, title, year_made, post_date, expire_date, user_name, description etc.
One fact table to store custom string, int, float, date field values of ads.
One fact table to store custom dropdown field selection values



Concerns and issues:
Looking at the schema, it seems to be a STAR schema with multiple fact tables where all core lookup tables connected to the main Pivot table and
custom lookup table connected to the 2nd and 3rd fact table.



Quick search only queries the Pivot fact table. While Advanced search query requires to join 3 fact tables. Both query requires to join 3 fact tables with all
dimension tables(15 to 20 each having avg of 20 values) to get the look up names so that users sees text instead of ids. 
Search speed is the Main concerns. Insertionupdate speed doesn't matter that much as that is less frequently done.