Reply to Organizing music library with iTunes + MBP from scratch [Need some help & advice!]

Hey everyone! I've been DJing for a while, but a big problem of mine is that my music library is terribly organized. When I started I decided to organize everything within regular maps, but this system isn't really working for me. After doing a lot of research here on the community and on other places, it seems that the general consensus of music library organization is:

Edit ID3 Tags > Analyse in Mixed in Key (or similar) > Import in iTunes > Import to Traktor

I wanted to make sure I did enough research because this is a largely asked topic. However, I'm still not sure how to approach this from my situation, which is why I made this post.

My situation:
So currently I have this fairly large music library with different genres and not always correct ID3 tags, organized in different maps.
I have two computers:
- a Macbook pro for DJing live
- a Windows desktop where I usually download music and practice in my bedroom (bigger screen).
- I also have a new unused External HDD which I bought some weeks ago but haven't used yet.

My questions:
1. What would be the best way to approach this situation? Should I edit all the ID3 tags first, then analyze everything and afterwards import everything in iTunes? I've also read about smart playlists which I will definitely use, but I believe the ID3 tags need to be fixed before I import everything to iTunes

2. Are there programs or scripts that could help with editing the ID3 tags? Going through all files manually will take a lot of time.

3. Any tips how to do this between two computers? I like using my desktop because it is faster and has a bigger screen, so I usually download songs there and practice my DJing. Of course I need my library on my macbook because that's what I use for DJing live.

4. I've read that it can be very convenient to let iTunes copy all songs into the library on import because it makes sure that you have all songs in one place, and then organized inside iTunes with playlists. Would you advice this? Is it easy to maintain two of those libraries on two computers?

Question 1 is by far the most important question, the other 3 are optional. Hope you guys can help me as I'm very eager to get my shit together haha! Thanks in advance.