Hopefully someone is able to help you, but If you have trouble with the modpack crashing, take a look at the crash log and find the badly behaving mod. This way you can slowly make it more stable. Also I recommend a mod called FoamFix, to reduce RAM usage. Hopefully you included all the required core mods also.
Aether 2, I wouldn't play just yet, it has tendency of crashing and lagging, as it still in alpha stage. Aether Legacy is more reliable and polished.
Just enough items (JEI) is a modern version of the now dead Not enough items (NEI).