Great RDW for standard. I really like
Harsh Mentor as a sideboard, maybe even a mainboard 1-2 of.
Fling may have an
opportunity to shine with your
Soul-Scar Mage and
Bloodrage Brawler in the mix. If you do decide to go that route, Consuming Fevor becomes really good, as does
Lathnu Hellion. You have a plenty of discard which gives you plenty of madness triggers for
Fiery Temper, but maybe consider replacing two
tormenting voice with two
Key to the City. That would allow you to play
Fiery Temper on their turn for 1 mana, allows you to prevent a block, and gives you a source of continuous draw if their plan is to stall you out.
Thermo-Alchemist is great, but it really shines if you're mainly playing burn spells and only a few creatures (something to consider depending on how heavy removal is in your meta). If you do go mainly spells,
Dynavolt Tower,
Harnessed Lightning,
Lathnu Hellion, and 1-2
Bedlam Reveler are good choices to compliment it.
Having two
Hanweir Battlements I understand since you're running four
Hanweir Garrison, but I've often found more than one
Geier Reach Sanitarium to be a nuisance since it's legendary, requires you to tap and pay 2 to loot 1, and only provides colorless mana. Overall I see 4 colorless to be a bit much when you're only running 20 lands, but 20 is of course perfect for your curve. That's just my preference so if you're comfortable with it then rock on.
I know
Insult // Injury looks pretty conditional, but I've been playing it and I'm in love. If you do ever consider sideboarding it,
Glorious End looks very interesting and will really throw people off their game if it's a close matchup.
Sweltering Suns is another great sideboard choice for removal, as is
Galvanic Bombardment.
Magma Spray is good against a lot of embalm/
reanimate effects, so that's something to think about, too.
A solid deck overall, though. Good luck, have fun, and give 'em hell!