Welcome welcome to the BP universe. Glad to have you. If you want to connect personally jsut link up in here and we can move the convo off of this platform :)
That said, ill answer your first question. You would be correct in thinking Zillow or any other mainstream consumer facing platform like that is not the best place... you can get lucky but thats not good thing to bank on. Honestly, if you're just starting out your best bets are to grow your network.
Meeting realtors and selecting a good one that you mesh well with and that has the capacity to deliver the results your looking for based on what investment you want is a good start. Next, attend your local REIA as frequently as possible. Build relationships there. Learn as much as you can. Offer to help people for free. And be sure to tell everyone exactly what your looking for as an investment, you never know who can point you towards a deal.
There are other ways to source deals and tools you can use... im sure if you use YouTube University and dive deeper into BP you can figure it out.
Moving to your second question... There are many 'rules of thumb' you can use - 1% rule, 2% rule, 70% rule, etc. but at the end of the day for just starting out I think you should focus on running numbers and get good with that. Get good at estimating mortgage payments and downpayments, rehab costs, cashflow before and after expenses, getting average rental rate numbers. This way when you do come across a "deal" you can assess it quickly and pull the trigger.
When I first started I would look at the basics.
1. How much cash out of pocket will it cost me?
2. How much will it cost to set up and operate the asset including debt servicing/rehab?
3. What is the total income or cashflow I can attain?
4. Am I satisfied with the left over cash that I could burn in a pile if i chose to after all the costs are paid each month?