Auto-complete query using FULLTEXT mysql index

I'm trying to create a good match query for an auto-complete search box using mysql FULLTEXT index MATCH capability. I would like it to be very performance optimized and if possible flexible to typos and such (without too much work).

The search is for users, where each user has a name and a screen name. I would like to match a combination of them. For example if the user name is "Guy Kawasaki" and the screen name is "gkawasaki" than the query "gkawas" and "Guy K" will direct to him. Also, I would like the results to be sorted by a combination of the match score and a grade I'm holding in the table.

Currently what I've done is two different queries:

SELECT  *, MATCH (name) AGAINST ('+Guy +K*' IN BOOLEAN MODE) AS SCORE  
    FROM  
        users  
    WHERE  
        MATCH (name) AGAINST ('+Guy +K*' IN BOOLEAN MODE)  
    ORDER BY SCORE, grade DESC LIMIT 5


SELECT  *, MATCH (screen_name) AGAINST ('+Guy +K*' IN BOOLEAN MODE) AS SCORE  
    FROM  
        users  
    WHERE  
        MATCH (screen_name) A开发者_高级运维GAINST ('+Guy +K*' IN BOOLEAN MODE)  
    ORDER BY SCORE, grade DESC LIMIT 5

I'm not so happy with the fact that I'm using two queries and also not so sure regarding the BOOLEAN MODE and all the "+" signs. How can I improve this? What is the best approach to implement such an auto-complete?

SELECT  *, MATCH (name, screen_name) AGAINST ('+Guy +K*' IN BOOLEAN MODE) AS SCORE  
FROM users  
WHERE MATCH (name, screen_name) AGAINST ('+Guy +K*' IN BOOLEAN MODE)  
ORDER BY SCORE, grade DESC
LIMIT 5

You can just add the column names to the MATCH () part of the query.