The literally single biggest mistake that people make is to buy a class D property, because it was cheap to begin with, 90+ days on market and they were able to negotiate a "discount" - ask them a year later how that worked out for them. 

The biggest issue you will find with a local bank is the seasoning requirement.

The biggest thing I have learned is to pick your market intelegently.  

As far as the land itself goes utilities are most likely going to be your biggest due diligence item.

I have doctors that I invest for and frankly the biggest problem is convincing hem they are not the expert.

The 2 biggest down sides in Southern CA is 1) in Single family zoned areas ADU additions add a value far less than the cost of the ADU addition.  

Looking at AirDNA results, my biggest concern is occupancy rates, most of the calendars I look at have large gaps in them, and when you spend close to $500/sq. ft at current prices (in STR-designated areas), your property needs to rent well above 80% or you charge crazy nightly rates.We've also seen very few property management companies that charge less than 25% there (and 25% is rare), and some STR neighborhoods require you to use their designated PM (Desert Colors only allows Red Rock, and they are at 40% commissions - ouch!).

Share your biggest challenges when funding your deals, is it Interest rates, down payments, or something else?

Unless you own the house cash, in addition to the advice you've received, you can't just transfer a house from personal to an LLC without risking the option of the loan being called since the LLC does not have two years of tax returns.For new investors without cash to buy, LLCs are about the biggest cause of analysis paralysis out there.

One of the biggest mistakes that investors make is they are not clear on what it is they want to invest in, and what their goals are with their investments.