1)Try that and you will see. There are many slightly different endings.
2)It is possible to find out if you replay the game
3)Simply put and without many details. Howard started researching forbidden books and cults as a hobby but soon discovered something bigger through them. That he can gain superhuman powers and control over others. Simply enough he decides to go deeper into all this, joining a brotherhood (this will be probably in the sequel) that shares the same interests. But nothing is simple when you go beyond reality and his quest for power becomes quest for survival. He sees conspirancies against him everywhere, he feels otherworldly forces are out to get him, so he decides to use his new powers to save himself. But while he is alone he doesnt know how to do that. For example he'd like to make minions that share half man intelligence half demon awareness, but mostly fails (that is a simplified example with poor word choice). These actions would seem that he went insane to a normal person. That is all simply put, I got bored of writing so I stop here.