Replacing spark plugs

You can drain about a half gallon of coolant to a clean container so you can reuse it.

And the car is NOT running properly if it is only running on the battery.
You said after you connected the hose, it started running fine.
But only on the battery?

??????????????????????????????

 

Do not remove the intake manifold or the EGR system! You need to first get the engine running like it was running before you replaced the spark plugs. Working on a different part of the engine will only make things worse. You do not want to go down any more rabbit holes. You seemed to go down many rabbit holes with the Gen 2 that you previously owned.

 

If you don't know when the coolant was changed last, you might as well change it now. Drain coolant before removing EGR parts. But if you don't want to go that route, don't worry about losing too ouch coolant. May be a cup or two will come out of the hoses. Just refill the reservoir to the top line.