I would consider a blanket and portfolio loan as you gain more properties. 

Flip is another word that people use to mean sell but after it was held as a long-term investment.The intent is important here as it will determine whether the sale will be eligible for a 1031 exchange or if the gain can be eligible for capital gain treatment.Best of luck.

For example, if I were to purchase a home for $1M, fix it up then sell it for $1.4M, how much of that $400k gain would be taxed?

Now I eat anything I want and have trouble gaining a pound.

If that is the case, then you will be paying on the capital gains taxes of the sale.  

Constant housekeeping complaints, bookkeeping errors, them using my property for their personal gain without me knowing it, charging outrageous "fees" that they didn't share with me, which effectively lowered my rents, and questionable repairs and maintenance expenses and quality. 

However, if all the properties gained the same appreciation, say 5%/yr, that would mean that the 1st REI would have gained $5k in PV/equity after the 2nd year, while the 2nd REI would have gained $25k in both PV and equity.IF you start with the same $100k in cash, spent it all, and look at this from the perspective of percentages, you would have the following:  100% equity vs 20% equity from the start, the 20% equity gives you a better profit, total PV and CF.1 - Cash flow that is 10% of the PV vs 5% of the PV, the 5% of the PV is greater than the 10%.2 - 80% debt vs 0% debt, the PV is greater for the 80% debt.

Are you asking this in regards to holding periods for capital gains tax calculations ST vs LT?

So the next important question is when would you like liquid access to your investment gains.

Look for areas with high tourist demand and strong rental yields, and consider attending real estate seminars to gain insights into the latest trends and strategies.