Your going to face the hardest boss in the game with a +3 pyro glove good luck with that I was stuck there for more then two weeks. If you have the DLC look up how to access it now because its coming up soon and if you miss it you have to play two thirds of the game again to get another try oh and the painted world is available from you might want to look up how to get into that I was stumped for a good while and eventually asked here.
1. I played through it twice with out finding the great hollow you will have to defeat Sif to complete the game though.
2. Not sure but you can have two copies of the same spell so if you can buy the fire spell again and attune it you can have 16 fireballs.
3. Seams very flexible some people go back and play again with out levelling up once any build can beat it.
4. I found that I needed heavy armour but if your a master dodger you can get away with light armour, seems a little unbalanced to me though. As for weapons you need to get your Pyro glove up. Not sure where that guy went he always just sat there in my playthroughs but there is another pyro teacher very well hidden
5. The +x after your flask refers to how much health each flask refills not how many extra flasks you have.