1. You can shrink and expand columns, but there is a max length for the columns for the editor. Best way around it would be to copy the table/columns to excel and edit it there. Then afterwards, paste back in the appropriate parts.
3. Why sum of recieve and transmit? Unless you have half duplex circuits, makes more sense to divide them seperatedly. Average should be fine but one possible issue (NOTE only applies if you are using custom SQL) is that for thirty days, there might be different "sizes" for the data depending on retention rate. As in, some will be for daily, others hours, etc. This will give the closer data much more weight if just using aggregate functions without grouping. (using the built in conditions automaticaly groups them, so only really a problem if you are writing custom SQL).