From the airport's website:
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">The luggage storage unit is located on the arrival floor of the terminal and is open round-the-clock. Passengers are charged a daily fee which is calculated after the collection of the luggage. The fees are as follows:
Big size package 10,000,000 TL per day
Normal size luggage 7,000,000 TL per day
Handbag 6,000,000 TL per day
Small size package (plastic bag etc.) 4,000,000 TL per day
</font>
As the previous poster noted, I doubt you'll see much trouble. It's a pretty cosmopolitan city, and the touts are amateur compared to say, Morocco or India. I was told to watch myself on the bridges, but then, why would you want to walk across a bridge, when you could spend the day buzzing back and forth on the boats, with breathtaking views of the city?
The visa/bandrol process seemed simple enough - the $100 is steep! I know for UK visitors, the £10 must be a newish, English (not other UK) £10 note only, so it may be worth checking out exactly what the requirements are for this. I was impressed by the efficiency, though!
As for what to do when there... Well, I enjoyed simply wandering, hopping between boats, drinking apple tea, Turkish coffee, and smoking from a nargile. It's a wonderful city, I hope you enjoy yourself.