I do understand the appeal of Fanatic, but there just isn't that much devotion to be had in a deck like this. The other big problem with him, is that he costs four to drop. God forbid you start the game with two in hand, and never even get to actually cast him.
With the BTE, while it can be an essentially 'free' creature, it's not that good of a creature for this deck. It's real job is to generate devotion, which it does pretty well (I play Devotion to Boros in standard) - but - a vanilla 2/2 for two in RDW just doesn't cut the mustard. A lot of times, you'll be casting it, and having the mana empty from your pool because you have nothing to spend it on. While it can chain out into dropping a Fanatic for 7 or 8, it's just not consistent enough to rely on, and to give 8 slots in your deck to.
Flame slash is a pretty good removal spell, but it is a sorcery, and it can only target creatures - which makes a dead draw in a lot of scenarios. I might keep them in the sideboard, but one extra damage isn't really worth all the drawbacks in my opinion.
Honestly, another card to consider is Young Pyromancer. You'll be surprised how effective YP can be with a good burn suite at your disposal.