From what I quickly read in the link above, seems like you just need to have a bank account that is govt insured and earning interest, doesnt have to have the tenants name on it, but you need to inform the tenant of account and rate the account is receiving. 

So if they pay more it is not that they pay over market rate.

These situations often require immediate attention that might not align with your available hours due to the time difference.Regarding property management fees, these can vary widely and you might find that the rates are more reasonable than expected.

So the point of this is that what often occurs is that in the year that you close on your purchase you start out at the seller's old property tax rate.  

They mentioned that the rate will be higher if locked for 5-6 months.

I’m sure audit rate on this has to be astronomical and just need good records?  

It requires the borrower has significant experience and is very costly (in terms of rates/origination)It's generally really risky to do 100% financing especially if you are inexperienced.

The challenges include - Interest rates - that are as high as they have been in 20 years; property values - which have doubled and tripled in the past 3-5 years.  

-will I be able to keep my interest rates?

It is tough to "perfect BRRRR" here with consistency or anywhere for that matter with today's rate and insurance costs.