1 - Melee range is 0. You are correct, this was a previous rule that I missed in a few spots.
2 - Yes, no limitations on that!
3 - Bosses grant you R3. I see now that I missed that information when talking about bosses. You also gain XP (page 28).
4 - Ignite does stack! It is one of the more powerful effects. Spending 1 Action removes all Ignite.
I'll add these to the FAQ/Errata document. Thanks for letting me know!