Test the coolant. Drain the oil and inspect for light brown sludge or separated coolant in it. Check inside the oil cap for pudding like sludge.
As for the knock, listen with a stethoscope to determine where it's coming from first.
The oil leak from the upper, front could only be a few things: Valve cover gaskets, cam seals or between the head the lower timing belt cover. Check the valve covers for loose screws (do NOT over tighten them). If that seems fine, pull the timing belt off the cam gears, remove the cam gears and pull the upper rear timing belt cover to inspect the cam seals and the seam where the head comes down onto the lower, rear timing belt cover.
Oil pressure on these cars isn't very high. 5-30psi at idle (kinda broad range there, huh?) and 40+ over 3000RPM.... <---- Not the exact figures, but they're some around there; Look in the TSRM for specific figures if you need.
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