I'm currently playing season, is there a way to expand vault or inv without spending $$? Also any tips to which char is best for beginner would be great ty

I haven't played in years so there might have been updates since. I didn't even know they have seasons now.
No way to upgrade vault without real money, sorry.
To play the game proper, you will really want a nearly maxed out pet, thats where your money will be spent.... or a LOT of your time.

I dont know if there is such a thing as "best class". Depends on your style and what dungeon you're planning on farming. Priest and Knight are good for most dungeons. I personally liked the rogue but i wouldn't say its a good starting class.

i tried playing melee like warrior, knight and pally.......holy i cant do it lol, died so many times, and the melee playstyle is so unforgiving, so little time to dodge things lol
ill try priest again, healing seems it could come in clutch