Haha, glad you like it, a lot of effort has been put to it. Ill try to answer those questions
Technically it works in any mode, just that all the inspiration has been founded from playing in adventure mode. Especially regarding all the tool restrictions. So i would recommend start playing it in adventure mode without the bonus chest. Thats right, no tools to start with. The player will receive levelup rewards as he progresses. When he first enters the world he will technically levelup at 0, and that reward is a wooden sword, player guide and a map. He should the try to survive with only that until he reaches 10 xp, gain level 1 and get as reward the wooden axe among a few other rewarding items. (There are plenty of ways to do it and even a legit way of getting wood without the axe if one really starts to think about it... )
In creative mode some things work differently. Placing torches will be normal, in survival and adventure they become torches that burn out. Also trying to open a locked door or chest in creative mode will notify the player with a chat message the required key code. I think ill put another post explaining the keys and locks.
Implemented so far:
Magic Missile
Fireball
Summon Lightning
Drain Life
Burning Hands
Light
Night Vision
Calm (undead)
Invisibility
Breathe Water
Fire Resistance
Flight
Feather Fall
Shield
Summon Skeleton
Summon Zombie
Summon Ghost
Healing
Some values are already modifiable and disableable in a config file. Once the mod loads up first time it extracts some script files including the config into folder 'mods/qadom/scripts/js'.
When i get enough feedback of things players want to modify i can add that.
Definitely has been planned but has been a lower priority. The ghost served as a study in how to do it, when time permits more will come. As said effort will shift now towards world creation, npcs and quests.
Absolutely.
Well, as this doesn't touch vanilla code it should be quite safe. But to be honest i haven't tested with other mods so cant say for sure.
No parts of vanilla minecraft has been messed around with except changing the max potion stack size from 1 to 16 (and there was a way to do it without modifying minecraft code).