[@Cassowarysaur]
Try to watch it to the end of episode 3 before deciding on whether to continue it or not, since the first 2 mislead on the actual content. 
I admit the art style can be an acquired taste, but it is deliberately that way to be deceptive. The writer Gen Urobuchi (Saya no Uta, Fate/Zero) in fact lied about the show being regular, innocent fare.

As for your questions: 
1, Yes it's the genre. 
2, It's not specified what kind of animal Kyubey is when it's introduced, but it's revealed later. 
3, That's standard for cute seinen, and actually one of the only fanservicey-things about the show, considering it's a seinen starring cute girls. 4, What costume do you mean? If it's the one Homura wears at the end, it's because she's actively using her powers at that point. 
5, They are in middle school, and are confirmed to be aged 14-15.