@Brendan Bruno there are many answers to the questions you are posing, but truly it depends on each deal independently. Many times, the "gurus" and other investors will tell you what they consider to be requirements to make a good deal, but it truly depends upon what your buyers are looking for. What may be a horrible deal for a flipper may look like a great deal to a buy and hold investor. You need to evaluate each deal yourself and determine whether you feel there is room there for you to make money and for your end buyer to also profit.
The leads can come in many different ways, such as direct mail, signs, cold calling, etc., but it depends on your style and what you have budget for. I can tell you from personal experience that the investors that put in the work and really hunt for prospects are the ones that consistently get deals. If you are just going to do what all of the podcast, YouTube videos, articles and books tell you, then just be prepared that you have everyone else around you doing the same thing. If you are able to differentiate yourself, then you will find that your success rate will be much better.
Buyers are everywhere, and they are easy to find. After a while they start finding you! A good buyer's list is important, but you don't want to spend all of your time building your buyer's list to some "target" number. The important thing is to get prospects and work to close them. You'll find that often your buyer's list will start to clearly identify specific buyer(s) that are consistent and as long as you have good deals there is usually someone ready to buy.
I don't personally double close here in WA, and stick strictly to assignments, so I can't offer up much in the way of pros and cons. However, there are some articles here on BP that discuss this, so just do a search and you'll see some discussions about what to expect for double closings here in WA.
Good luck to you in your adventure, and remember the most important thing is to start doing. Everything else falls into place, and you'll learn more from doing deals than you ever did in a podcast or other learning modules. You can make good money, help out a lot of people, and have a lot of fun, but make sure you are working ethically, honestly and with the intent to help people. If you do this, then you will experience sustainable success. Don't fall into the shortcuts and traps that have given Wholesaling a bad name in the industry. Let me know if I can ever be of assistance.