Locate the pressure gauge after the prefilters and before the membrane housing. That's after the vertical filters and before the horizontal big one....
Yes you will have problems with the fittings leaking. Don't feel special tho, I know tons of people who have had the same problems. Remove the tube from the fitting and check that it's cut square and even. Push it back into the fitting making sure that the tube is seated completely. If it's not the tube section leaking, unscrew the fitting itself and apply teflon tape. Reinstall the fitting making sure not to over tighten.
If those don't work, post a pic, maybe I can give you a hint....
RandalB