There is a lot of dangerous information floating around this thread for a new rider... I'll start by answering your gas mileage question, the smaller the engine, the better the gas mileage. A ninja 250 should easily get you over 60mpg, most 600's will range from 40-50mpg, and 1000+ bikes will range from mid 30s on down. The hayabusa is a 1300cc bike and will not get amazing mileage.
The danger in starting with such a fast bike is that it will bite you in the ass the second you make a mistake. Slip the clutch accidently on a 250 and the bike will rev up and start moving away in a fairly controlled manner, do the same on a busa and both you and the bike will be on the pavement before you can blink. I would honestly be suprised if you could successfully get the busa out of first gear on your first attempt at riding a bike.
One person posted earlier about an r1 (1000cc bike) not wheelie-ing as easily as an r6(600cc bike), however this is just the opposite. The r1 may be a bit heavier but it has so much more power than the r6 that the front end will lift up with much less effort, this can easily catch a new rider by suprise.
For new riders I definitely say that smaller is better for your first bike, smaller bikes are more forgiving when you make mistakes, they are lighter and easier to maneuver, and they get incredible gas mileage. Also, you can typically sell smaller starter bikes for about what you paid for them in the first place.
I took the safety course because it came highly reccommended from all the riders I knew and I believe it was completely worth it. I learned to ride a few years before taking the course but they teach you a lot about emergency maneuvers and really help you get an understanding of how to properly ride. The small 250cc bikes they let you use are so nice and light that they really give you a lot of confidence in riding. The first thing I noticed when I got my 600 was how much heavier it was and how much harder it was to turn, especially in tight spaces. I am still working on perfecting a lot of the drills I learned from the course on my 600 and its not easy. I'm willing to bet that 90% of the people who think that the course is a waste would fail the riding course on their own bikes.
As for gear:
1) Full face DOT approved helmet, This could range from $50-$700, the difference in price results from better venting systems, nicer liner materials, more custom fit, higher quality graphics, etc. But DOT is a standard safety rating system, so any DOT rated helmet is as safe as another DOT rated helmet. Some nicer helmets also adhere to stricter requirements like Snell approval.
2) Jacket. For jackets you have 3 major options, leather, textile, and mesh. Leather provides the most protection but is usually the most expensive option, it also gets hot in summer months, but some jackets provide perforations or vents to help cool you down. Textile jackets are usually nylon based and feel like thick ski jacket material, not as heavy or hot as leather and usually have zippered vents. Mesh jackets are similar to textile but the fabric contains thousands of holes to allow air to flow through and keep you cool, these are more comfortable in hot months but do not usually provide as good of protection as leather or textile jackets. However some brands offer mesh jackets with textile or leather reinforcements in critical areas like elbows and shoulders. Also look for jackets with CE approved armor in the shoulders, elbows and back (this is standard in most riding jackets).
3) Pants. At the very least wear jeans, but you can find riding pants in the 3 jacket variations listed above. You can also buy jeans or cargo pants with reinforced knee, hip and butt sections.
4) Gloves. Gloves are very important because when you find yourself falling you almost always put your hands out to catch you.
5) Boots. You want boots that come up over your ankles, this will help protect you if your pants slide up your leg in a crash. As a side note my buddy went down wearing a pair of untied DC skate shoes, they flew off as soon as he hit the pavement and he couldn't walk until the road rash on his feet had healed.
Sorry for the long post but riding is serious shit man. You need to keep a level head about it and protect yourself. A popular saying regarding gear is "dress for the crash, not the ride." Be safe with whatever you decide to get.
