It sounds like you already have some concerns about this company or you wouldn't be asking these questions.
The first item of concern is the HDMI cable. There are only two types of HDMI cables - standard speed and high speed. The high speed HDMI cable can carry any signal currently in the HDMI spec, easily including 1080p. The standard speed cables are only guaranteed to carry 1080i or 720p signals but usually can do more. For a passive
High Speed HDMI cable, the maximum distance available is 25 feet. For an active high speed HDMI cable, the distance can be expanded beyond 50 feet. Since they specified 35 feet, that means the cable they are using (assuming it is a passive cable since they didn't say anything else) is a standard speed HDMI cable. So there may be situations where that cable cannot handle signal you are trying to send to the TV. It may also be the reason they have problems with ARC.
See Monoprice Redmere cables for an active High Speed HDMI cable that can handle 35 feet.
In-wall power should only be installed by someone certified in the installation, such as an electrician. The cable should be rated for in-wall and should look like typical house-wiring cable and should never be an extension cord. So that's one thing to check there.
If this is going into a brick wall that is part of a fireplace, be careful you don't mount the TV too high. I have seen many an installation where the TV is so high because of a fireplace that it becomes unwatchable from neck strain. A lot of money gets spent for something that isn't enjoyable because no one thought about being able to watch something that high. Usually the fire place (while it seems like a great idea) is a bad place to mount a TV.
Digital optical will provide a compressed multichannel audio signal or non-compressed two channel signal. This is acceptable for satellite/cable TV since that's all they send. Also ARC only allows a compressed signal anyway, so it really won't matter, particularly with a sound bar. The only possible concern is with audio sync with the video. You won't know until you try that out if the audio is in-sync using optical. It will also depend upon the source.
Finally, HDMI switches are fine. It is a digital signal. So it's the same 1s and 0s whether there is a switch or not. If those 1s and 0s don't get through you won't get a picture. Just make the switch can pass-through 3D, if you plan to use 3D movies.