Hi, you should not add extra data to Megapack or the MegaGlest program directory. Instead, work in the directory which contains user specific data ("UserDataRoot"). There, you can either create a copy of Megapack and add to that or just create a new techtree which only includes your new factions. Since Windows users have often trouble identifying and accessing the UserDataRoot directory (because Windows uses a complex and, by default, partially hidden location there), our Installers do, since MegaGlest 3.5.2, add a start menu shortcut to make accessing this directory easier.
The errors you are showing in the last screenshot are caused by bugs in the XML files of the factions you added. You should ask the modder who developed them for help about this. If you prefer to look into this yourself you can use the --validate... command line options to megaglest.exe to get more information on what is going wrong there.