I gut over 6 deer a year, did one Saturday in CT.....
Your overthinking, it's pretty easy to do. Go slow the first time is all, once you get the incision made carefully, go ABOVE the Liver cut two sides of diaphram to access the heart lung cavity, then cut windpipe as high as you can. Then work everything out from there making your cuts toward the back of the cavity pulling and roling everthing out as you go.
Small very sharp knife is all you need. I use the Butt out all the time now.....it does make the job quicker, but not needed really. If you have the Butt out start with that, stick it in and twist, then SLOWLY pull out...working back and forth...if you pull out too fast you'll rip the canal. Once the canal is loose there's you can tie it off, but there's really no need, it will come out with the intestines pretty readily.
If for some reason you hit paunch or guts with either the knife arrow or bullet, it's really no big deal...just messy, and smelly I wash it and dry it out with paper towels and it's usually pretty OK. But certainly take your time and avoid hitting the paunch if its not touched by your arrow or bullet.
If you wash the cavity, Water will grow some bacteria if left in there, best to dry the cavity with paper towels as much as you can, that will inhibit things growing in the cavity. Generally, this is not too much of a problem, because the deer should be left at 38-40 degrees.
But if things warm up....growth could be a problem....