Hi and Welcome to the forum. Please understand what I'm about to say is not meant in any way negative however it is truth.
First, we understand the joy and pleasures that come from owning these trucks and how nice it is to be able to do the work one self. It is rewarding and comforting at the same time knowing you did it.
What you need to understand before jumping off the cliff of parts purchase is there are some important things to establish and know.
FIRST OFF.... READ the FAQ section THOROUGHLY then re read it, this way you will have a good basic understanding of these trucks from a theoretical knowledge.
SECOND OFF.... READ the TECH section THOROUGHLY then re read it, this way you will have an even better understanding of these trucks and how to do some of whats needed.
THIRDLY... READ the HALL OF SHAME section THOROUGHLY and learn where NOT to spend money!
Your enthusiasm for your truck is admirable and I like to see that in a young fellow such as yourself.
Take heed though that these trucks can be $$$$pendy if you are not wise young grasshopper and start tearing into stuff without a true grasp of all that's involved.
As previously mentioned, an open discussion with Typ4 would be in your very best interest. Sometimes, as much as we want to do something, having someone who has done it and does it well is better, for example rebuilding your turbo.
We are here and very willing to help you in anyway we can. The collective here far surpasses the general knowledge at the local dealerships and shops that service diesel trucks now a days, we specialize in these trucks pretty much like no other.
You have described your truck and mentioned it has been beaten. Maybe it's time to step back, get it down to a truck shop get it steamed off or pressure washed off thoroughly or do it yourself top to bottom front to back and get it clean and easy to see leaks and work on as well.
You mention leaks galore including HG how do you know the HG's are bad? What has brought you to this conclusion.
Please understand there is a lot going on, take the time to slow down, provide thorough and precise information and pictures too. We are much more able to assist with information when we have all the information.
Again welcome to OB read read read and once you have read lots, go back read more, there is tons here.
Al