The “secret sauce “ is that there is no secret sauce. True, there are many different aspects to note investing— it can’t be learned by the seat of your pants. That said, it’s like learning anything else (at least in my experience); you just put one foot in front of the other.
Of course you're going to run into "analysis paralysis" when starting out with anything of any complexity, and the note business is no different.
You would do well by just concentrating on the marketing end first, say, by developing effective ways to source "plain vanilla" performing notes, secured by either SFRs or commercial property. Line up an established funder who accepts referrals, and just submit (using their request-for-quote forms) the inquiries you get. You've got to be detailed on the clerical side, i.e. "dot the I's and cross the t's". If you don't know how to evaluate a note yet, don't worry a lick about it-- just submit. The funder will reply (provided you properly fill out and submit the forms) and if they aren't interested, they'll tell you and also they'll tell you why... keep asking your "dumb" questions and keep submitting potential note transactions until you start to recognize the good from the bad.
All of this is not costing you a dime. Just a little time.
It's like anything else- as @Chris Seveney said, most people quit ANY business when they realize it takes work and perseverance. You've got to have "stick-to-itiveness". But it doesn't have to be hard. Spend just a few hours a week honing your marketing skills, continue to develop your note sourcing methodology which is the #1 skill you need to succeed. If you can FIND quality notes, there will always be a buyer for it and a way for you to connect. Do this properly (they key is PROPERLY, as referenced in many discussion threads here) and you can earn money using "other people's money" as you're asking your "dumb" questions and gradually finding the answers.
Takeaway: Just concentrate on marketing first. Don't worry about the other stuff yet. Trying to analyze potential deals without having a purchase option agreement in place is really a total waste of time. You need enough volume (inquiries) coming in order to do business. Like any business, this is a numbers game.. for every X # of responses, you will get a certain % of "takers" and, after that, you may have a certain # of transactions that will not go through for various reasons-- so keep churning, and don't waste your time with 'paralysis of analysis"; when you get a preliminary agreement in place and your funder begins the due diligence (pre-purchase) process, THAT is when you start following more closely-- and for the transactions that ultimately close, you get a nice check AND you're getting a million dollar education for free.
Keep things simple, just keep doing this over and over, and when you've referred at least a handful of notes that close, you've then built up a file and you're going to start to recognize most, if not all of the steps involved so that you can begin to invest in notes for your own account. Sure, there are unique "issues" with any transaction but the funders are going to show you what's good and what's bad and you're learning by osmosis.
One more thing: When you get responses and submit quote requests to funders, be sure to fill out the note submission forms properly and completely. If you're sloppy and/or incomplete with the paperwork, you may not get responses. What I like to do is get out my financial calculator and work the numbers on the note detail I get from the potential seller to ensure that I come up with the same numbers that they have given me. You also need to confirm the EXACT present balance, # of payments made and # of payments remaining... and if this looks like a good note (which you will eventually learn to recognize as you become more experienced), I almost always ask for copies of the note, mortgage and closing statement. Go over them and verify that the numbers line up with the numbers on the submission form.... If the potential seller will not or cannot share these items with you, walk away. They're not serious sellers. You've just screened them out as a waste of time.
"Time is money".