Hi friend,
As
@Mbrooks420 shared, I would take a good look at the timing cover gasket. This is a very common leak point at the age of your vehicle, at the top of the the corners of the timing chain cover where the coolant goes in and out. If you pull the water pump, I would definitely do the timing chain cover gasket and while you are there, the timing chain and gears as well. All parts relatively inexpensive.
The pulleys in the belt routing are all wear parts, there are 3 of them to replace from my memory, do them all if you have not already. When they fail, you will be on the side of the road.
I do not know your maintenance history but if it were me, heading out on a long trip, I would consider the fuel pump assembly at this age/miles if it has never been replaced along with a complete tank cleaning (you need to remove the tank to do this)
As far as the EGR valve, are you getting codes? You do not say why you want to replace it and yes, it can sort of be difficult to get a good grip/angle on both the threaded connection to the exhaust manifold (I have used a crow's foot to break this connection) and the small bolts actually holding the EGT to the intake however, it is not that terrible of a job but I am not sure why you would want to replace it?
Surging idle could likely be IAC valve. Easy, inexpensive to replace. Cleaning the MAF sensor may help.
As far as the passenger exhaust manifold, the bolts to the head could be an issue, depends. I have replaced several of these and did break one off but it was on a vehicle that had a significant amount of rust. I ended up drilling it out and re-tapping but this can get tricky. Again, you did not say why you wanted to replace this, I am assuming you are getting a tapping / clicking sound and you can see the carbon tracks somewhere on the manifold / head where it is leaking? In any case, the real trouble bolts are the ones connecting the manifold to the down pipe to the exhaust. On the passenger side, these are a real pain to access and you may have to cut them off. These bolts pretty much get a build up of corrosion and combined with the heat cycles and combustion gases, they are very, very stubborn to remove, even with a lot of patience, penetrant, heat, etc....
I cannot tell from your description what your are talking about in the "left frt wheelhouse near core support". Maybe additional description or a picture will help.
Funny thing, I am now down to owning / servicing 3 of these 5.0 - 4R70W drive trains and I would trust going across country in one of them more than I would my recently purchased 2.0 Ecoboost Twin Scroll Turbo - 6F35 drive train.
Good luck,
3.
