[Tucson Quadplex] First deal, feedback please!

[Grant Olsen]

Asking Price: 245,000

Turn key fully rented quadplex built in 2000, no required improvements in a B neighborhood

Total Rent: 2950 which is already the mid-high end for the area so I doubt there is a potential value play.

Property Tax: 2200
Insurance: 1100
Utilities (water): 1680
Maintenance+Property Management + Vacancies estimated at 30% of rent

This comes out to 44% of rent = planned expenses which is pretty close to 50% rule, so passes sanity check.

Monthly Rent - Expenses: 1,650
Cap Rate: 8.02%
25% down with 3.875% mortgage for a 15% Cash on Cash return
Cash flow: 786

To check my math against rules of thumb:

50% of rent: 1475, 
payment on a 0% down mortgage: 1161
Cashflow: 314, or about $80 per door

Using my calculated expenses net rent: 1650
payment on a 0% down mortgage: 1161
Cashflow: 489, or about $120 per door

I plan to initially offer $220k which would price the cap rate to 9% and cashflow up to 875, but I think the property is a reasonable deal even at asking and currently am prepared to pay retail price. Any thoughts?

Additional Questions:
1.) Is the standard 1 month vacancy still relevant for quadplexes? should I up that a bit?
2.) s 10% of rent on maitenance for a quad reasonable?
3.) Should I just forget about the minutea and just use the 50% rule?
4.) What is the lowest cap / return that you tend to accept in your area? This is one of the best deals I've found (on MLS) in Tucson after months of searching, but am considering branching out to other areas.

Thanks in advance!