Surprised you don't have a reply - are there no MS SQL Server gurus in this forum?
For what it's worth - based on my Oracle experience:
a) it depends on the number of non-NULL, distinct entries in the column indexed
b) if they are all non-NULL & distinct, then 10% of table size per index is typical (depends on rowlength of course) - this can mean that a complex table (many indexes) has more index than data!
My GUESS is that MS SQL will be about the same.
You're going to have to create indexes on that table . . . . DaPi - no silver bullet