Hi @Bryan Schwartz welcome to BiggerPockets!
Happy to answer with my own personal experience though I'm sure everyone has their own opinions and ways of doing things and ultimately whatever works is what works for you
1. Did you use traditional marketplaces like yelp, thumbtack, angi?
Personally I have not had the best experiences with these sites, I typically go via word of mouth referrals from other investors I know from in-person networking in my market, or from the BiggerPockets referral tools. Those who are marketing on BiggerPockets specifically know the investor mindset and specifically want investor clients vs the typical homeowner.
BP doesn't have a "finder" tool for everything yet, just agents, lenders, tax pros, PMs and Syndications, but there are more being added! And once you find an investor friendly agent, they probably have a good referral for an investor-friendly painter, and an investor-friendly painter may have a referral for a good investor-friendly electrician, etc.
2. Is it common to protect your list or are you open to sharing with fellow investors your know?
I believe in community over competition personally, that's just my philosophy so I treat my workers really well so that they prioritize me and respond if I'm ever in an emergency and I share my referrals with friends and other investors who I am familiar with and they do the same for me.
3. How do you store it? Google sheet? Do you use software?
All my properties are in a small regional area so I only have 1-2 people per task I need and I have all their numbers saved in my phone. For me it's that simple but I'm sure folks with more properties or properties in different areas have better systems than I do!
4. Do you have multiple for vendors per trade?
I have my primary person and then a backup. My primary people have been good at referring others to me generally - like when my handyman was on vacation, he referred me another handyman when I had a need that had to be tended to within a few days
5. How or where have you typically found the best contractors? Online forums? Referrals? FB Community Pages? Nextdoor? etc.
Referrals from other local investors, and also referrals from other homeowners in my area on local facebook groups!
6. Do you perform regular preventative maintenance to avoid emergencies or are you more reactive?
Regular preventative maintenance, typically during turnovers between tenants I take note, anything that will likely be a need to repair in the next 12mo I try to fix during my turnovers before a new tenant, but I also take note of anything that may be needed in the next 24mo and the next 5years and I estimate the cost and budget it into my reserves
Best of luck with your self management journey!