Quick question about Warband, mods and achievements

There is no problem with sync. Warband mods doesn't overwrite files and you can play vanilla (you chouse Native or some mod from the launch screen). About achivments, you can get some of them even when you play mod. May be even all of them, depends from the mod. If the mechanic that is connected with the achevment is in the mod, you will get achivment. If it's cut from the mod, then you need to play Native or other mod to get it. In example there is achivments connected to marriage, but some mods remove the marriage and you can't get this achivment with this mod, but you can play Native or other mod (you can have installed all mods that you want in the same time, the only limit is your disk space and there is no conflicts between them). The game is very mod friendly :) The engine and the content are separated. Even vanilla is like mod called Native.