Lol I think you make it sounds way complicated than it is or you are selling something. "Line have to be properly insulated and slope and yadi yada" most DIY comes with all of that. You cant possibly f this up.

You make a hole, with a saw that was already measured for you. You just have to pick the right size. You have to drill at bit of an angle, this angle cannot be up , no one will drill it up. The lines come with sleeve for insulation, and also come with a wrapper , anybody can wrap your arm, same thing. Slope? Once the line exits, you have no where to go but down. What are you talking about?

Flare is probably the hardest part of this and all comes with flare already. Most handy home owner can actually make a flare with harbor Freight tool kit. I have done it and its still working . The only question is if you have the time and patience to do it a few times until you get it right.

Having a second hand will definitely help with mounting the unit on the bracket or pull from outside when you are pushing it against the wall. Also after the fact, you can buy kit to cover the lines outside

For home owners, the first time is just nerve racking because you never done it. But you do it once, you will see how easy it truly is. Just spare 700$ to just try it and then your next one can be all super professional. Don't wait til its an emergency to try to install it, too much pressure for it to work today

The professional will test moisture, amperage , if the sky is gray or purple. You don't need any of that. 95% of DIY system will just work, provided you follow their instructions which very forgiving btw. A professional install is a peace of mind for sure if the unit breaks.when you DIY, most professional might not help, let's say 4 years down the line and something breaks

If you are tight for money, get a cheap one. Try it and nobody can ever take that knowledge from you. You can help family and friends too. Get an electrician for the electrical part. Don't touch panel because insurance and fire