Bruce has provided the definitive answer.
The order of fields in the summary window is as defined in the key fields, followed by the Item fields and then, quite logically, the calculations which are dependent on the previous order of data groupings.
If you need to present the results differently the easiest thing might be to export the summary to a report file and then pull that into another Monarch session as a table to change the order of the columns.
As far as the negative values displayed as zero is concenrened, there are circumstances where that might occur naturally - (small negative decimal numbers where no decimal places are defined in the output format for example) but logically that can result in some key level summary values that do not seem to total to the summary of summaries. If this was extended to all negative values I could imagine the problem woujld be much greater.
Once again you could use the export to a report file and revise in Monarch to creat calculated fields to change negative values to zero where you wish to do so.
I can make no comment on whether it is wise and sensible to do that in a report. I assume that provided it is not for audit and accounting purposes there will be no harm done.
The only other thing I can think of is to change the colour of the rows that show a value less than zero - but that does not seem to be quite the thing you need to do.
Does this help to explain things?