I am an Investor Agent in the Tampa Florida area and I found joining local REI groups through Meetup.com and Facebook. 

We currently are in the process of building this, and we have more projects that we are working on for other partners to join.

As for the nextdoor app, I joined the neighborhood where I bought my last property (Woodmere) and neighborhood lead was saying my account was going to be deleted because I don't live in the neighborhood, but I showed him the nextdoor app rules and that was the end.

I'm excited to join this vibrant community of real estate enthusiasts.

I could do all cash with perhaps some help from family (less than $15k) or friends/partners (one has asked me to find something he could join in on with $20k, the other serious one has about $35k-$50k to invest with me). 

You can also join FB groups and see who the most recommended contractors are in your area.

Are there specific forums, events, or associations I should join?

@Kristoffer Ruohonen I have an online commercial multifamily group you could join and am just about to launch a German/European one as well since many many parameters are much different in these countries.

If not, I would suggest looking into / vetting one (happy to refer if interested) and joining local meeups (meetup.com and facebook investor groups).

Joined Bigger Pockets several months ago.