for me the grind starts at level 25+. that's when you have to grind at F4 all day.
plus there's alot of grind as well if you want to hunt for set equipments ( i'm too cheap to buy it off other players ) but if you're not interested in set equipments then you can just grind F4 mission map.
quests are pretty much useless. they give you some silver.. very small amount of exp.. the only quest i bother to do is the hero quest which is the main quest ( everyone has to do it anyway.. )
there's cash shop in IAH version as well. so far, the cash shop is not over-powered.
they only provide exp booster, insurance scroll ( to prevent your equips from breaking when you soul craft/refine ), revive items, megaphone, costume, etc.. nothing spectacular..
but in the future, it might get over-powered..
i just found out today that you can actually soul craft costume cash shop and get like defense/evasion option but the costumes still have expiration date.