96 Legacy Wagon Oil Pump & Sensor ?'s

Was told I have low oil pressure and need oil pump. Is this a very difficult job for a deliberate driveway mechanic. I've done tune ups, shocks, brakes but Timing Belt in particular makes me nervous, water pump and oil pump replacement and all associated seals. Can the belt simply be replaced by aligning hash marks with corresponding timing marks or is a light gun needed?
Knock Sensor & Throttle Position Sensors - Can these just be switched out and replacements plugged in? Thanks for any help