The spell combo mechanic was mostly inspired by some Final Fantasy games, the order for each given spell is the same so after a few tries it's not too hard to learn the order, since they are pretty short.
The fight in the game are designed for combat classes. Most of the player stats also come from armour, weapons and accessories. Once sufficiently geared most of these fights become extremely easy. With a decent set of armour and a score of 5+ in INT stat, a magic user can defeat 2-4 Werewolves before needing to restore health.
There is a way to cheat XP in game for those that find progression too slow. You can use the cheat sheet to get infinite money and then buy infinite Skill tomes from a Succubus in the Brothel on Saturday to get infinite XP. I initially didn't even have Hero mode as I set XP accumulation rate based on personal preference. Most people found it too slow so I introduced Hero mode... which some people find too slow as well. At the end I just added the Cheat Sheet so people can use it to get however much money they want and in effect as much XP as they want. This way the player can just set their own reward/progression because it's the only way I know to just appeal to everyone.
As for Player Leveling. Player level in this game is his Rank in the Demon Queen's army, it will go up to a maximum of 5 (currently planned) based on main story progression. The first Rank Up quest is being worked on now for the next big update!