The Eco has an 8 gal DEF tank. When mine gets to half full I refill with the 2.5 gal jug. That brings it to 6.5 gals full and precludes any overfill message.
DEF is 33% Urea and 67% deionized water. Your 2017 has a DEF Quality Urea Sensor that will trigger a code at 22% Urea (78% water)...
It would help if you gave an "overheating" coolant temperature number and the conditions during the overheating. The coolant temp gauge does not measure the coolant temp, it is an algorithm number derived from certain engine factors.
I have seen some high temps as you have. In every case it...
To answer your question #1, your best option is MRT Stage 2 tunes and EOC delete parts, all via EOC. If you cannot do it yourself, find a local shop to do it. It's not hard, just labor intensive.
Here's how
Pull out the starter relay (in the fuse box).
Put the key in the RUN position.
Take a short piece of wire and jump between where pins 30 and 87
of the relay would go. if the relay is labeled 1-2-3-5, jump between
pins 3 & 5.
I have no experience with Tuner Depot but can say if you want to turn off the EGR the GDE compliant tune does not do that. I'm running the MRT, via EOC, stage 1 tune that shuts off the EGR. It has a handheld device that allows you to select their 20hp or 40hp tune or change back to the OEM tune...