The pump is in the tank and the tank is under the seats. There should be a plastic mesh around the pickup.
Pressure test requires a pressure gauge and fittings which you can buy as a kit. Flow requires pulling a line and measuring volume pumped per minute. Shouldn't be too hard to find instructions on the web.
Like I said above, your fuel pressure regulator is not integrated into the fuel filter therefore you need to change it separately. At this age, putting on a new pressure regulator would not be a waste for the same reason you replaced the fuel filter. It fits your symptoms.
http://www.realoem.com/bmw/showparts.do?model=AM33&mospid=47718&btnr=13_0737& hg=13&fg=10