If you have a 100 cash flowing units you won't have to have a reserve.

You'll need enough to cover down payment, closing costs and 6 months payment reserves. 

Items like vacancy, future maintenance reserves, etc. can be variable along with your mortgage numbers depending on what financing you obtain. 

All contracts, options, or other devices not based upon a substantial consideration, or that are otherwise employed to permit an unlicensed person to sell, lease, or let real estate, the beneficial title to which has not, in good faith, passed to such party for a substantial consideration, are hereby declared void and ineffective in all cases, suits, or proceedings had or taken under this chapter; however, this section shall not apply to irrevocable gifts, to unconditional contracts to purchase, or to options based upon a substantial consideration actually paid and not subject to any agreements to return or right of return reserved.

I just lost a $1000 1 month reservation within minutes of the lady checking in because the guest found a single hair in the sheets and what looked like couple flakes of dandruff or crumbs.

I have 40k in cash, reserving 10k for rehab.

That is just my take though vs. putting more down and having less cash reserves.

To elaborate, I'm referring to making sound financial decisions to best position their available capital and reserves for the future.

To approve the loan we will need to verify that you have $45,000 in total cash reserves, this is to insure you have at least 6 months of payments left in your account after closing.

I wasted my time at auctions where the bank set a reserve price, don't tell you about it, and I get a letter in the mail saying "no go" because the bid is under the reserve price.As to how banks look at it, the mortgage due is the determining factor.