Help analyzing a quad, 50% rule still applies?

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Hello all, need help seeing what I'm missing. I'm a loooong time reader/watcher and first time having a seemingly perfect opportunity fall into my own back yard/ neighborhood. 

Been looking for a tri / quad forever in my little town and boom, this morning it hit the market. 

4-plex, all under one roof.

210k sale price

8 bed / 4 bath *Four: 2/1's 700 sqft. No garages or car ports

Rents are $600/each, $2400 total.

Expen$e$:

P&I: $1055/mo (FHA 3.5% down @ 4.6APR for 30 years fixed) *can't put any more $$ down.

Trash: $40/mo.

Prop taxes: $3500/annually or $292/mo.

PMI: $165/mo.

Vacancies: (Est 10%) $240/mo.

Management: (Myself) $0/mo.

CapEx & maint: Estimating 50% right? *This is the sticking point, everyone says its a good rule of thumb but does it apply to quad's? as that's $1200/mo., seems outrageous for a small quad under one roof. Current status of prop is descent, no major cap-ex in sight.

So if that adds up i'm negative $-592/mo.

Help me confirm if this is correct or if i need to not count 50% to future cap-ex & maintenance. 

Thanks!