[PS2 games not working]

On retroarch, you need to find where you installed the program on your computer, within that directory you should see a folder called "system" All your bios files should go in there.
However, you should use PCSX2 emulator to play PS2 games and not retroarch. In that emulator, look to the top of the screen to where it says settings, then select bios option. From there you need to define the folder where you have the bios saved on your computer.
The error you are seeing is mostly likely because of the emulator not being set up and not a launchbox error.

[Horizontal and Vertical monitor at the same time]

Let me know if this rabbit hole is even worth pursuing or possible.
2 monitors side by side: monitor 1 in normal horizontal aspect ratio and monitor 2 rotated on its side in a vertical aspect ratio.
Launchbox with theme such as big details where monitor 1 shows the game list and monitor 2 shows the details of whatever is selected.
If a horizontal dominate game is opened, instance 1 of the emulator loads on screen 1 displaying the horizontal game.
If a vertical or cocktail game is opened, instance 2 of the emulator is loaded and game appears on screen 2 in vertical aspect ratio.

Thanks.
 

[In the process of ordering my parts for my cab and have a question about mini-pc’s.]

Not sure that computer has any GPU power at all, you will not be able to play anything that has 3D graphics, so things like the Xbox would definitely be out. My guess is that PC will max out at PS1. You also want more RAM with that much going on.

[Achievement Badges keep disabling themselves]

Using big details theme, I find that I am constantly having to enable the "enable achievement" badge.  It keeps disabling itself for whatever reason.  I can force the issue to happen if I make a software error, such as combine 2 selected games and then click on old one whilst it is still active on main screen. But it also seems to be disabled on software launch and other random times. All other badges don't seem to have an issue.

[RetroAchivements Question]

I have submitted the request to add the alternate name  ~Homebrew~ 8-Bit Rhythm Land
to the launchbox database for you. 

[RetroAchivements Question]

Perhaps the alternate name needs to be published to the games database and then it will work?  I assume that is why Alter Ego works, launchbox recognizes and links it.  Adding only to your local association won't help in that case.

[RetroAchivements Question]

I believe Launchbox requires the title to be named exactly the same as the retro achievements site does in order it to display the tab and sync properly.

In your case, retro achievements names the game   ~Homebrew~ 8-Bit Rhythm Land

This can be very annoying for showing achievements for home brew and hack versions of games.

[King's Quest CD, Playing in LaunchBox without a CD]

The older King's Quest titles have remakes that work much simpler and don't need dosbox at all, that is what I use.

[AHK Scripts location]

Will this help?

 

[Searching for metadata on Emumovies takes way too long?.]

same here, curious if older version of Launchbox takes 5 minutes as well.

[BigBox isn't loading the arcade platform]

In Launchbox, did you remove the "arcade" category or the arcade playlist? You should have a category that says arcade that if you open the triangle will reveal the arcade playlists, which should include "2-player games", "4 player games" then "arcade" again. I got into trouble once by removing the arcade playlist from the arcade category and then big box stopped working correctly.  My thinking at the time was why do I need an arcade playlist to show all games when I can just select the root folder and get same thing I thought it was redundant, but Big Box did not like that at all.

[BigBox isn't loading the arcade platform]

Did you try selecting "View Platforms" in the menu and then use that as a starting point.  It will give you a breakout of arcade, counsels, handhelds, etc and then you can determine from there why your play lists are messed up.