> 1. if 2K can be changed to 8K for this buffer pool?
You should be able to create an 8K i/o pool, then drop the 2k pool by setting its size to 0.
> 2. If add another 16k buffer pool, should Affected Pool be changed to the right pool?
If you don't specify the Affected Pool (when calling sp_poolconfig), the procedure uses the pool with the smallest i/o. So if you had an 8k but not had dropped the 2k, the space for the new 16k pool would come from the 8k pool.
> 3. How to decide then pagesize, configured size and wash size for a buffer pool? Are they part of total memory size allocated for this cache?
The wash is included in the pool. I don't think it usually needs to be adjusted.
Which page size pools to have will depend on how the cache is used. Tables with a clustered index that have a lot of range queries will benefit from larger page size pools, as will text/image/java. Syslogs is said to do well on a 4k pool.
-bret