My ride is a 2005 Suzuki SV650s – Vtwin sport bike. But I rode a C50 a couple times this past month, which I know isn’t the same as the S40, but it’s similar in design (the S40 is a single, approx. 650cc, the C50 is a Vtwin, approx. 800cc, but the chassis is essentially the same).
At rest, the C50 feels very top heavy, something that won’t be as much of an issue with the S40. But once rolling, the bike handles very well. Well mannered, predictable, smooth (though if you’re used to lofting your body over bumps as on a sport bike, the feet-forward position will take some getting used to). I think I’d term the handling as pretty effortless. So in that regard, the bike is great for a beginning rider. With the 650 single, you might get a little more vibration, but it won’t overpower you. This would be a good bike for more well more than 6 months — you may well get years out of it. It’s far better to ride a smaller bike to ITS limits than to ride a larger bike beyond YOUR limits.
I’m 5’9″ and small change, so you’re a little taller, and a little lighter than me. I don’t think you’ll find the bike cramped, nor do I think it’ll be too big for you, but by all means, SIT ON THE BIKE and decide for yourself.
Kelley BLue Book on that bike is $2745 (http://www.kbb.com/motorcycle/retail/2006/suzuki/s40/79454), so I wouldn’t go any higher than that, no matter what aftermarket stuff may have been done. The asking price is fair as long as the maintenance has been done, and it starts and runs smoothly. But that’s just my opinion.
Hope that helps.