Hello, sorry for the late reply. For fast leveling you can do solo quest which give max EXP gain instead of bring your companion which EXP will be shared. You can also buy potion at place of beginning for 1.5 fame for 1 level
In this video, it take a long time to get level 100+. Maybe around 150 hours playtime since I still learn the game mechanic I started new game+ with only ability transferred, and take 35 hours to get level 200 mostly from solo quest (annihilation, subjugation), high level boss may give 30% EXP per kill, buy elixir from place of beginning will give you 1 level per 1.5 fame. Underworld maybe another good place to get EXP since mobs there are high level and usually give 5% per kill. Maybe there are another way for fast leveling but I not sure, nothing good come from leveling too fast unless you want to beat post dungeon quicker
Either dancer or hunter. Dancer is you can spam element song to do damage around you, hunter is for dark arrow and poison arrow which dark use to blind so you can attack them for far safely, and poison to kill boss (assuming boss not immune to poison) As for shaman I think it's status ailment class like casting poison, blind, silence, etc and not really have any offensive skill. And battlemage is kind of spellblade which infuse your weapon with elemental attribute so you give extra damage corresponding to the element
