IMO, using leverage is a matter of timing when you want the income from a portfolio.For example, the more leverage you use, the more your returns will be (assuming you hold long enough to even out fluctuations) because appreciation on your leveraged property will usually provide more wealth than any other element in real estate investing. 

Numbers wise, I use 5% vacancy and capex, maintenance fluctuates between 5 and 10%, and 10% PM fee.

Cambridge has had large fluctuations of population growth over the years but I would say on average it has growth 1%.* Majority of cities had a population growth of about 0.5% in the first half of the 2010s* All cities have a trend of decreasing population growth* Springfield had a small growth in the first half of 2010s (population is 154620 people in 2015) and in the second half of 2010s, its population declined (population 152646 in 2020).* In 2018 population in Newton City and Lower City started to decline.

I recalculate rents once a year after calculating for property tax and insurance cost adjustments as well as market fluctuations.

The market as a whole there tends to trend about one year behind the Seattle market, and not have as large of market fluctuations.

One difference between the two, is once you find out your close ratio from the lead service provider, that number is not likely to fluctuate, and there's not much (that I'm aware of) that you can do to improve the quality of those leads.

But since the market is not dependent upon bank lending, the prices don't fluctuate as much as they do in the US.  

STRs have very regional number fluctuations vs LTRs.

It’s a market that has fluctuations but it’s drivable and people flock here.

Waiting the seasoning period in order to refinance allows rates to fluctuate (a con in today's environment since they have been increasing seemingly everyday)There is a lot to learn with BRRRR and surely a ton to love and to be weary about.