Could you confirm the operation and maintenance figures for varying sized generators?

The best data I have on diesel O&M cost come from Alaska, where labour is expensive and the climate is harsh so I think of them as the high end of the possible range:

So the O&M costs for the 400 kW to 800 kW range are on the order of $14/hr.  That is probably too high for your situation, but $0.06/hr is certainly too low. 

In the cost spreadsheet, be careful to specify the O&M cost of $3/hr, not $3/hr/kW.  In other words, do something like this:

Don't do what I sometimes see people do, which is this:

That would make the O&M cost $1800/hr for a 600 kW diesel, which is not what you want.