I feel like it wouldn't be too hard for me to make a 10k-30k mistake on my own in the school of hard knocks. 

Worst damn money move of my life!

While I would never invest in NY as James mentions as its the worst - if I was going to do it I would atleast make sure I tried to follow the rules. 

We've made mistakes along the way, but nothing so detrimental it put it us out of business.

Remember that you can only get one home equity loan per year, you can only have one home equity loan on your home, and you cannot convert your home equity loan into a different type of loan, so choosing the wrong loan can be an expensive mistake that you cannot quickly fix.Time Factors: If you need money quickly, don’t forget the schedule for closing a home equity loan, and make sure you will have time to complete the process, close on the loan, and wait through the cooling off period before you have access to the money.

And someone jumping into this as a complete newbie can expect that they have a decent chance of making some expensive newbie mistakes.

I am going to rework it and have it as 'worst case'.

Just because you don't make any money on them, doesn't mean you aren't responsible, along with the source of the actual plans, for any mistakes in the plans, or even any mistakes in construction from lack of info, misunderstanding, or just plain stupidity of the builder/user of the plans.

Side question: How can you help ensure a good, timely, mistake free lending process? 

It's a very common mistake where an investor sold and bought properties and then when it's tax time they find out they didn't do the right process to actually qualify as a 1031 exchange.