How to create YouTube home guitar demos from parallel taken phone video and professional recorded PC audio? (please consider, I have zero video recording skills, neither know video editing software. What I know is no more than there are video/audio codecs, container formats, streams, and I also aware that video/audio sync could be a problem)

Context

I would like to create acoustic guitar demos of my home playing.

Sound quality do matter, so audio of simple iPhone video recordings will not do it. I have established practice how to record guitar audio (with my mike, amp) and I have also established audio recording practice, this question is not about this)

Now I would like to do video too, not just the audio.
My very first idea is concurrently record video with my iPhone, somehow transfer to my Windows 10 PC, and then edit the video and (put and sync?) the high quality sound with the video together.

Question

Q1: Is this a good idea? (I've checked how to connect my iPhone cam with PC, but it seems no benefit, it has delay, quality loss, etc)

Q2: I would not like to do sophisticated video effects and postprocessing, however I would like to have multiple recordings (multiple audio/video takes, for example to compare guitars), and "switch" between them (10 secs from one, then 10 secs from other, then back) in the final result. The two streams from two sources (audio and video) must be synced, but preferably not the price of sound quality, video quality is not so important. What free software (Win 10) is recommended for this task?
Bonjour Pickardou!
What you want to do is absolutely manageable and done by a lot of people every day. First, let's talk about the "sync"-part.

On professional movie-sets, you might have seen the movie slate. It's essentially a board with some text on it that can make a slapping-sound. This slap is used exactly for this purpose of syncing. When you recorded both audio and video separately, you then load both in your editing software, find out where the "clap" is in your audio and sync that to the frame in which the slate claps. You could do the same by just clapping with your hands.

To the second question (switching from multiple cameras):
Yes, you can totally do that once you have a recording of multiple cameras - just drag all views on top of each other on a timeline (use premiere or sony vegas to give a few examples). So now you can just cut off the top-layer which will then show the bottom layer, which would be another camera-angle. Do all of that and you got yourself a nice music-video in no time.

I hope I was able to help, have a wonderful day :)