A few questions

[eastman51]

Hello, I am new to the forums. I bought my 95 SC 2wd back in February of this year, and its had a ton of problems. Started and drove reliably, but whew, so much wrong. I've finally caught up on a lot of things, but there's some stuff left to do and would like some advice on how to proceed.

I'm looking to change the transmission fluid soon, and originally wanted to do a flush. But at 226k miles, I'm wondering if that's a bad idea. But I think I should at least change the filters.
I'm also going to change the supercharger oil, probably just with AC Delco if that's fine.

I know my SADS couplings are torn and there is some play in the shaft, but zero noise and the accessories seem to run just fine. I'm seeing on the forums that some kind of BMW coupler is good, but you need to modify them to fit; however I seemed to only see that on posts for earlier year vans. If the later years have larger bolts, does that mean you don't need to modify the BMW couplers?
I'm also going to change all the V belts and tensioners when I do the SADS couplers eventually.

I am fairly certain my oil return pipe leaks. The whole bottom of the engine is covered in oil. I have already changed the valve cover gasket, and that does not seem to be leaking anymore.
And the transmission mounts are tearing.

The things of my more immediate concern:

The coolant in the reservoir looks a little dark, and I have no idea when it was last changed. The van reaches and maintains temperature just fine, but I do want to change the coolant for good measure. I also want to replace as many coolant hoses as possible; or at the very least, the primary radiator hoses and any other hoses that are prone to failure. I'd rather not let my headgasket die because I didn't replace a $2 hose. I would also replace the thermostat.
Looking in my FSM, the water pump looks to be really easy to swap out. Should I replace it while I'm already servicing the cooling system? I believe my oil filter pedestal also leaks, so maybe I should just since I could already be there?

The EGR. I tested the EGR components under the seat, and they hold vacuum. My code is just the flow insufficient. I already took the air inlet off and cleaned that side pretty good; but I remember not being able to remove the EGR. That stupid flare nut on the pipe going back to the cylinder head is seized on there good. I could spin it with a lot of force, but it didn't really move easily; I also broke my 3/8" u-joint trying to loosen it.
My CEL has not gone away, so I need to take another stab at cleaning the passage. My idea was to unbolt the EGR from the intake and remove the EGT, then fit a carb cleaner can's hose between the EGR and the intake, then spray and pray.
The other issue I have with the EGR is that after my last attempt, it started to make a high pitched noise. I think it comes from that giant flare nut, since I don't think I moved the pipe around with enough force to bend/crack it. My thought was to use muffler repair paste or exhaust RTV around the flare nut to hopefully stop that. If I ever had to replace the EGR, I'd have to cut it off regardless.

My ac does not work because of a leak at the union up front between the drier and the ac compressor I believe. The pipe on the drier side of the union has a gash that goes behind the flare nut, so it leaks all refrigerant within a couple days. I have no local junkyards with a Previa, and you cannot get this pipe from Toyota. Not entirely sure how to proceed on this.

I will be taking the van back to the dealership sometime next week. I had them rebuild the differential due to a bad bearing a few months ago, and its still howling. At the time, my flex pipe was completely busted and the exhaust was just a mess entirely; but now I have put a new exhaust on and the diff howl is unbearable on the highway, and very annoying while slowing down in any situation.

Edit: I am also probably going to make a custom harness for the headlights. Mine are effectively useless, despite doing a Chrisfix headlight restore and brand new bulbs. Good to know its a common issue though!
I believe I saw a wiring diagram on the site that is supposed to sell harnesses, but I will have to look it over again.