First things first get an extremely through inspection on the truck. Ive seen carmax vehicles with hidden damage before. Any good diesel shop should be willing to help you out there.
As far as acronyms just ask.
You might want to do more research the number to the right of the W is hot weight left is cold weight. So 5W-30 and 5W-40 have the same cold flow properties just one is a little thicker at operating temps.
There are multiple people who have installed them. B&W and Curt both make ones for our trucks. Just be mindful of your payload capacity, it would be easy to overload your truck.
AFE makes a larger engine oil pan it holds about 2 extra quarts which helps cool the oil system.
PPE makes a transmission pan which has replaceable a filter and is made out of aluminum instead of plastic. Which well be less expensive to service and more durable.
This is the best place to get your led lights from. They are tested and confirmed to work with our trucks. http://cftperformance.com/ram-1500-2014-2016/
The first thing you should do when an oil cooler fails is to pull an oil sample and either test it your self with a hot plate set to 200 degrees Celsius. Or send the sample off for testing, personally I do both. If there is any free water in your oil it can damage bearings, turbo, etc.
There is only two things that well really help with the throttle lag. First being a proper ecm tune which I recommend PPEI 20hp tow tune. Second being a throttle booster BD diesel makes one thats well liked. The water methanol really helps with mid range torque while towing and it lowers egts.
If the failed oil cooler is found early then that repair is perfect. But yours was possibly missed long enough to cause issues with your three way valve and that's dangerous. My first step would be to get an oil sample and test it for free water. If there is more than about .5% your bearings...
Glow plugs are very easy the first one calls for 1.1 hrs then an additional .2 hrs for each from there no need to pull the cab. Now the turbo is a whole different animal it's a big job.
Running a dpf back exhaust well do nothing for sound really but it well help lower egts a little. So its not for nothing its just really hard to notice.