multiple event handlers fifo grouping

We're looking at implementing FIFO grouping, but it may be complicated, and we're curious about combining more than one aspect of processing, thus our subject; multiple event handlers fifo grouping. 1) Is it possible or is it to be avoided? 2) Will the different handlers manage the fact that their grouping may not be based on the same fields as other handlers? 3) Will thread usage remain constant across different handlers; imagine we set max to 16, will handler1 always use the same amount? thanks jb.ext