advice for a first time braider!

hi all,

i'm not Black, but have learned to box braid and braid cornrows on a mannequin for a few of my friends. however, i do have a few questions, as i've yet to braid outside of a mannequin head.

1. in preparation (scalp oil, heat protectant, detangling, blow drying hair) where should the scalp oil fall in order of these steps? do i need to have leave-in conditioner or another type of moisturizer, and when should that be applied?
2. im planning to braid my teammates' hair for cross country meets - our races are 3 miles. I'm not concerned of the security of the braids, but outside of braid/hair gel, should i be aware of any products that can help reduce frizz through high impact sports? is there any precaution i should take for not making the braids too heavy?
3. where should i source good quality synthetic extensions? I bought some off of amazon, but found they were rather difficult to manage in comparison to human hair. is there a better alternative or should i just expect that buying synthetic extensions online? i do have beauty supply stores near me, but they do not have the colors that i need.
4. anything else i should know? thanks in advance <3