Noob here, need helpI

I'm fairly new, and I'm a bit confused about a few things, so I have a few questions:

1. Do weapons just change the playstyle? (besides changing stats of course) For example, with the Pyromancer, you'd obviously play her as a fire caster, right? But her second weapon is focused on electricity, so should I be changing my playstyle based on the starting spells of each character? Like thrust for Assassin, holy for Paladin, etc...
2. Are there secret passives? The Hound Master, for example, spawns hounds, but I couldn't find any information on how that works or when it happens. Do other characters have secret abilities like this?
3. Should I focus on looping in the beginning, or is it better to increase the difficulty as fast as possible before looping?
4. Is there anything else that’s worth knowing?

Thanks in advance!