I have been riding for many, many years. I suggest you do not get a bike. You will very likely get hurt- really hurt or worse.
If you are stubborn, do me a favor- if you can...go right now to Youtube.com and type in "bad motorcycle accident." It's rarely your fault- cars will pull U turns right in front of you- no possible way to stop and near impossible to avoid. If you can honestly sit through this for 2 hours straight, then go out and get the 500cc. I think it will fit you better and it has more power which can actually be safer to get you out of the way of the car. Extra power is only a problem if you don't know how to ride. You can get just as dead on a 125cc bike, if you do not learn how to control the power.
The other poster is 100% correct- if you are going to ride, you need to first learn to ride correctly by taking a professional safety riding course on a borrowed 125cc or scooter. Learn slow and in an area without trees, curbs, poles (of any kind, etc.) ALWAYS wear FULL gear whenever you ride. Do not try to keep up with more advanced riders and don't go too slow in traffic either- also dangerous. In 100 degree temps I had full leathers, full face helmet, gloves, boots, etc.
Other tips:
Loud Exhaust is a must.
Don't top off your fuel- it overflows onto the rear tire by design- slippery
Toll Booths are oil slicks- you'll go right down
Dont downshift in a turn- wheel hops and you can crash
Always install a steering dampner to prevent tank slappers
STICK TO A CAR WITH 4 DOORS AND A SEAT BELT!