I have a friend that buys and sells quite a bit in SoCal.

This triples your headache.BE the voice of REASON to your friend. 

I started using both at the same time and found AirBnb to be far more user friendly with less clicks/swipes needed for any task.

it is mostly from what I've been seeing in activity in my STR, and in talking with some friends who manage restaurants.

I do already have a construction crew run by a friend who fixes anything that needs attention before renting out.

A friend of mine is a successful wholesaler, so I asked him how he does it.

Start with your closest friends and family but they will invest with you because of your relationship not necessarily because of the real estate or your real estate acumen. 

I have a friend/neighbor that wants to sell me his house below market value so he can move back into an apartment and travel.

I was debating if I should partner with a friend or family member who is willing to work on a property together. ill be sure to make sure things are done legally and fairly so no one get short sighted and things don't get messy.

Through friends.