1. The necessity for the back boxes on the mid and rear speakers.
2. The need for high end HDMI cables. I know I need 2.0's but do I need Forest 2.0's?
3. From the TV down to the BLU-RAY player everything is Wi-Fi and everything has to be hooked up to the net for firmware updates and such. The whole thing sounds too complicated. I think the Best Buy rep said that he would turn off all of the Wi-Fi except for the TV. Does that sound right.
4. I am paranoid with the whole smart tv means "they can see and listen to everything you do" kind of thing. The rep said not to worry since the TV does not have a camera. When I asked, "What about the listening?", lets just say my fears were not alleviated. Do I need to worry?
The TV is excellent and you should be happy with it. I don't love LG for their build quality, but the image quality is really top shelf right now.
1. Back boxes to help control sound bleed and provide proper audio is common with better gear. They sell this as a secondary item to allow that upgrade option. If you have the means, then I wouldn't pass it by.
2. No, you don't need high end cables. You DO need, and want a path from your TV location to your equipment location. I would recommend 1" to 1.25" conduit. If you are having all this work done, why not put in a way to add/remove wiring in the future if you need to? You can pick up cables, or ask for HDMI cables which are $20 or less for a cable. Maybe $25 or so for the long cable. I'm not sure why you need 2m and 3m cables if your equipment is all just a couple of feet apart. I typically use one or two six foot cables, and one or two three foot cables. Never longer unless I'm in a full size rack. Then 9-15 feet from the equipment rack to the TV. Typically I pull two cables just because it is easier to do at the time, and an extra 20 bucks for peace of mind is a good thing to do. Complete cabling should be less than $100 for HDMI and achieve standards to accept a 4K signal.
3/4. Yes, everything hooks up to the Internet and it should be. Your phone is, your laptop is, your laptop has a camera, your phone has a camera... Stop being weird about it, your phone and laptop are far more vulnerable than your TV or Blu-ray Disc player will be. Count on your cable box being pure Internet driven as it is. It's only complicated when you do NOT connect it to the Internet because it doesn't get firmware updates and it doesn't get proper updates. I almost always recommend that you hard wire directly to the Internet if at all possible. This provides a more reliable connection. You don't have to put in passwords or anything since it is hard wired, and you don't have any issues with streaming and buffering issues when watching Netflix, Amazon Prime, or something off your Roku player.
Get a Roku.
I would strongly suggest, before donating to a school, you find out if they have any need or use for the gear. A church 'youth room' may get better use out of such gear. A school often doesn't have the room or technical prowess to properly setup a A/V system, or even use it. Double and triple check on that as they may say "YES!" - but really not have any final purpose in mind.
Be aware than DefTech Mythos equipment still holds a fair bit of value. I have no intention of ever getting rid of my Mythos 8 center channel. The subwoofer isn't bad and if you are happy with it, then by all means, keep it.
You may want to consider a local installer instead of the corporate mega chain.
I would also ask, what kind of remote do you intend to use with this gear to ensure it is easy for the family to use? Surround sound and the rest is what the real 'complicated' part is, and when the wife or family can't use it because you need 12 remotes, or even one lousy remote, then things can feel pretty weak in a hurry.