I have a 1990 toyota celica gt hatchback STRUT RPLACEMENT

I won't address your struts question because you can find the answer in any service manual. Refer to the free repair manual for your car at www.autozone.com. Look in the "Steering and Suspension" section.

For your other two questions.

If the oil on the passenger side is leaking from down low it could be coming from the oil pan gasket. You'll have to remove the oil pan and reseal it with a new after-market gasket or with gasket-maker. If it is coming from higher up behind the timing cover, most likely it would be from either the crankshaft seal or the camshaft seal. Replacing these involves removing the timing belt and the camshaft and crankshaft pulleys. Refer to the service manual. Or it could be coming from the oil filter. Make sure that the filter is securely in place, and check that its gasket is in good condition, or just replace the filter.

The vibration/rumble is most likely due to old worn out motor mounts. You can probably eliminate 80% of the vibration by replacing the front right motor mount - the one that attaches to the passenger fender. To replace the mount, start by loosening the mount's center bolt nut. If I recall correctly it is a 19mm nut, and you will probably need to fit a steel pipe extension over a 19mm wrench to loosen it. Then support the engine with a jack before you loosen all the other bolts on the fender and the timing cover. .

Let me know if you have any questions.