The downside to the assumptions, in general, is that you have to occupy them for around a year, and you still have to come up with the difference in cash when you purchase. 

At the same time, I to minimize my downside in investments so LTR's would be a more consistent cash flow option (at least to me)Something my wife and I have thought about doing is at least reducing the principle balance so that whichever option we go for, we at least aren't losing money every month.Really looking for some clarity here as these next few years are going to be very important in order for us to set ourselves up well for the future.Thank you in advance for your thoughts and advice on this topic!

Do you see any downside to converting a garage to a mother-in-law suite?

The down side is the cost and financing. 

Im no expert by far . my thoughts would be if the rate is fixed and the property cash flows now then its only upside from there with rates, refi, value adds , rent roll increases ect. if there IS no cash flow at the current rate there are the down side to consider repairs, bad renter issues, ect ect .

IMO, the downsides far outweigh any potential benefits of renovating an occupied unit.

There are certainly downsides to Airbnb -- both to a city and to a landlord and neighborhood.

Any downside in using a HELOC with the BRRRR strategy?

But, we should all know and understand the consequences as well as the probabilities.Not picking on you Jon, but most newbies here on BP have never even gotten this far in their knowledge, but they want to jump into a barrel and start making their fortune without ever understanding the potential down-side (both probability and severity).

(because I built it).On the downside, I'm not an Excel expert, so I'm sure a serious Excel pro could create a model that's much better-designed than mine...and there are also probably programs that would be better-suited to the task than Excel (I just used Excel because I have some understanding of it, but I had no understanding of the other software options).