Personally I try to reserve my HELOC for emergency or unexpected costs during a project, so if you can try not to use all of it for the initial purchase and planned rehab.

My starting strategy is to do a few fix & flips to build some cash reserves up and then get into BRRRR in a couple of years. 

All monies from reservations we have get deposited into our account, and then at the end of the month we do monthly statements and pay our owners out of our account. 

I had another person try to bargain me down to $1700/month, and said she was moving out of her dad's house and so needed room to store boxes in the extra bedrooms. 

However, I see how one may struggle to change the email, since it may have important information stored or they've reached full capacity for making new emails. 

Cash reserves? 

If he has the income to support a $550k mortgage, and a healthy cash reserve fund, he should invest the money.

Changes some of my answer below, but here would be most of the types of transactions you would have in these accounts and between them.Property transactions would be: all property specific rents and expenses, allocated expense transfer to the master LLC and transfers to master LLC bank account for profit AND/OR property management fee.Master LLC transactions would be: Shared expenses going out, reimbursements/transfers from properties for their allocated share of those expenses coming in, the transfers from your properties deemed as profit AND/OR property management fee and then transfers to your personal accounts deemed as owner distributions.Other transfers that could occur is if the master LLC needs to transfer to the properties for capital expenditures above and beyond the reserves you might leave in their accounts.

Bifurcating the asset and operation, putting the wealth behind an "iron curtain" and arranging the public facing side of things in a manner where it is a conveyor belt of throw-away entities with little to no value stored themself, IS a viable approach. 

I'm curious how you handle situations where a guest wants to modify their reservation and leave early?