The loss between the filter and the tee is small compared to the loss over long lengths of pipe and through other fittings. Their design is fine and some perfer that over the single large pipe. Either way, the loss is nearly the same so I would not concern myself with that.

With that PSI setting, you have about 47 feet of head in your pool using 10 feet for the suction head. Now look at your pump curve in your manual to determine the flow rate.