Welcome to M3F! :wavey:
I have a 2008.5 automatic transmission 2.3L hatch and I've gotten one tank with an average of 26MPG and that was because it was a lot of idling and city driving. I usually get 29-31MPG average on a tank.
As a first car, it is definitely on the more expensive side of things. It's really hard to get much more than the mid 30s (MPG) with the 2.3L, insurance is quite expensive since it's made in Japan, and the mods you will do will burn up any cash in your wallet faster than you can say "0-60". :lol:
That said, if you're looking for a MZ3 as your first car, I'd suggest getting a 2.0L. I don't know what the engine with 300cc's has different, but it's not that hard to get 40MPG with the 2.0. The only downside is that in the US, the 2.0 only comes in the sedan and we all know that hatchbacks are better.
The 2.0 Mazda3i Touring is a pretty nice deal when comparing it to a Toyota Corolla or Honda Civic of the same year, and MZ3's in general are a lot less common (at least around here anyway) so it's easy to find your car among the sea of tan 4-door sedans. :lol:
Going back to gas mileage, honestly, your right foot dictates about 70% of your gas mileage. I learned most of the hills and turns around here to where I can coast when I need to and give it gas when I need to, and still get around 30MPG (city/hwy combined) with my 2.3L auto. I have a ScanGaugeII which I mounted in the ashtray to help keep track of fuel mileage and other stuff, and it also works as a OBDII code reader for any CELs that may come up.
Anything else you need to know? If you get a MZ3, you will become an addict to these forums. But don't worry, we have a M3F Anonymous in the Lounge, which I haven't joined yet since I've only been logged in for 12 days, 22 hours and 49 minutes. :lol: You will also, as I've mentioned before, watch your car vacuum all the extra money out of your wallet.
Seriously, if I didn't come across these forums, I probably wouldn't have gotten a MZ3, I wouldn't have any mods on it, I wouldn't know how to properly detail a car, and I would be a lot less knowledgeable on cars in general. There is a how-to on these forums for damn near everything from how to delete the parking lights to how to dismantle your dashboard and change the instrument panel LEDs.
EDIT: just read your new post. The 2.0 and the 2.3 are pretty peppy cars. I was also worried that getting a 4-banger car meant balls-to-the-wall to get on the freeway, but I barely give it any gas at all to get up to freeway speeds. For comparison, I drove a friend's 2007 Honda Civic, and on a long uphill onramp, I was flooring it and we were only going 35MPH by the time we got on the freeway. :shock:
I'd say that aftermarket support for the MZ3 is pretty strong. Intake, exhaust, chassis braces, interior mods, suspension, rims, turbos, etc etc are all very easy to come by.