'96 ES300 Intake Manifold Gasket Repair Questions/Advice

[Lvboo]

I had an oil leak that seemed to originate somewhere as high as the intake manifold gasket. I never exactly pinpointed if it was the front or rear. I continued to drive the car for about 6 months and just dealt with filling the oil (maybe a quart every few weeks) and placing a mat when I parked (laziness and procrastination cause us to do crazy things 😅). Anyways, a broken brake line ended up taking the car out of commission (in December, middle of winter in the midwest had to repair out in the snow 😖 not the most fun I've ever had).

So that's the backstory. Now I've had the car parked for about 18 months and I did the foolish thing and never ran it so the battery is dead and the gaskets are probably much more brittle as well as having bad gas, I'm sure. 

So I am looking for advice on my repair as to what other things i should replace and look to check while I'm halfway down the engine. Are there other possibilities as to where the oil was originally leaking from? If it was the rear main seal, which side would the oil be leaking on? What other components should I replace without getting too excessive? This is what I am thinking so far:

-replace Spark plugs

-flush coolant, oil + replace fliter

-Valve cover gaskets

-Front + Rear intake manifold gaskets

 

Suggestions I have seen:

-Water pump? (how necessary is this?)

-EGR valve?

-Timing belt?

P.S. I have done this repair on a '98 buick lesabre.

P.P.S. sorry for bad formatting or missing information, this is my first post.