I´d like to know about the fuel consumption of this car (2005 civic lx, d17a1)

I bought it used last saturday and I can see the fuel gauge going down very fast.

Before I bought it I measured the compressions on it and it measured 200, 200, 200, 195 psi

I changed oil today (using castrol 10w30)

The car is only 10565 miles (the lady who I bought it from said she was almost not using it)

I also changed air filter for a cheap equivalent filter (not using original one)

I´m sorry to ask but how many valves does this motor has?

I bought it just because I liked the quick pick up it has at the time of pushing the gas pedal

I´d also like to know (sorry to ask too much) if the d17a2 (vtec) is dohc?

Is the D17a1 an interference engine?

I mean, does the motor dies when the timing belt breaks?

One last thing...if I use iridium spark plugs, will it improve gas consumption?