The discrepancy of peak number of clients is explained by how many unique devices are connecting vs the amount of devices connecting at one given time based on the different time intervals on the graph. Because the time interval is more stretched out in the daily display vs the monthly display, you will have a more accurate reading of how many devices were connected at any given time during the day, but not how many unique devices. Because the monthly display has less time intervals to record, the same amount of unique devices have to be fit into a smaller time interval, thus you may see higher numbers in the monthly display, because while they had disconnected before reaching peak on the time interval of the daily display, they are all included in the larger time interval of the monthly display.
Download and Upload are reported based on the average of the network as a whole at the time interval. Because the amount of time the bi-hourly or daily are more stretched out than the weekly or monthly displays, you will see a more accurate to the hour average download/upload reporting on the shorter time choices, and a more averaged out view on the weekly or monthly views.