50% Rule Expenses

[Don Nelson]

So I'm estimating expenses and trying to figure out the 50% rule. I'm an experienced flipper, but moving to buy and hold. I understand the need for CAPEX reserves (5% of GOI) and property management (8% GOI), taxes, insurance, general maintenance (1% of property value). I'm planning on tenants paying utilities, HOA's, and won't buy in a flood zone.

So far, I'm up to about 34% of gross operating income.  

So, the obvious question is, what am I missing? Anything important or is my percentage low just because of my choices around HOA's, utilities, etc? Thanks in advance.