Reclass, any tips for OSUT as a Sergeant?

Yeah, don't be a douchenozzle to the new soldiers. You'll be an insert and only for the last third of the training. Remember these guys have been doing scout stuff the entire duration. They will more than likely know far more about being a scout than you do when you join them, and it would be wise for you to understand this fact.
Also, no one cares about your previous MOS, least of all the trainees. You can, however, take the opportunity to improve upon the OSUT experience for those young men by helping them to understand the army, be available to answer questions, and impart general knowledge.

Get ready to ruck...a lot. Get ready to not accept "Marksman" as good enough on like 12 different weapons systems and definitely not for your M4. As a SGT you'll be a Team Leader/Gunner, Truck Commander or maybe a Bradley gunner (all depends on what unit etc), so you need to know everything Joe does....and why it's important, how Reconnaissance works. You need to live the Fundamentals of Reconnaissance and you better know the 5 Types of Reconnaissance (RAZRS) before you even show up. Max effective range of weapon systems, grazing fire, plunging fire, Call For Fire, enemy vehicle identification (start with the playing cards...then graduate to thermal pictures), basic formulas for demolition calculations (cratering, cutting, counterforce, water impluse, field expedient stuff). Learn the history of the US Cavalry, NCOs are expected to earn their spurs (us cav starts with Gen Pulaski...hint hint).
Your crew served weapons you need to know like the Army Rank structure - as in you have to try to mess it up.
Drawing sector sketches, assessing routes and terrain, thinking of how the enemy would come into your AO.
This may seem like a lot but believe me (I was a Scout for 9 years), this just scratches the surface. There used to be Skill Level manuals for each MOS and I kid you not the LEVEL 1 manual for a 19D (E1-E4) that had everything a lower Scout should be competent on was thicker than the 11B manuals...ALL OF THEM PUT TOGETHER. You're an E5 and will be gunning (pun intended) for an E6 slot which brings on much more. The Section Sergeant literally runs half the platoon (PSG and PL aren't really in charge of much...one is beans/bullets/medevac/keep leash on LT, and the other should just sit with a handmike in his ear unless a signature is required)

A Scout is an amazing job, truly. It can be tons of fun, and a lot of physical work. The more you learn about RSTA the better you'll be and it will be noticed, I guarantee it. Many Scouts just think they do what an 11B does because we've been fighting COIN - which was exactly right. But they forgot all the actual Scout stuff. You have a chance to really bring the mentality back to "snoop n poop" "scouts out" "jack of all trades, master of none", etc

Learn the Scout Handbook. We commonly referred to it as the Scout Bible.