With this particular cut, which I mentioned before is like the middle-of-the-road option, the washer bottle is not overly exposed. I spray painted mine black at first, but I'm not in a hurry to do it again now that the paint is wearing off. It's just not that noticeable.
A heat gun will be helpful to manipulate the fender liner how you want. And zip ties are perfectly adequate for holding it in place if needed. I like using the zip ties, since they are easy to put on, they hold well, and if you need to cut them off to get in there it's no biggie to replace. Sounds like a hillbilly fix, but it's effective and easy, and nobody will notice.
Also, I wouldn't worry about getting your cut edge perfectly smooth. The edge trim (which I recommend, obviously) will cover it up nicely, no need to sand it down.
Your fog wiring will be more exposed, depending on what you do with your fender liner. Definitely a good idea to tuck it out of the way, but like I said, keep as much fender liner as possible to try to keep it covered. This was my mistake.
Other than that, there's nothing to it. Cut conservatively and then shave off more if you need, it doesn't work the other way around.
EDIT to mention: Wear safety glasses and sleeves. You'll get hot melting plastic sprayed all over you. It won't burn your arms or anything, but it stings. And you definitely don't want it in your eyes.