I would be scared of any windows server myself seeing there is still some unpatched exploits in 2k and 2k3. Probably none public but there sure are some. Some hacking groups hack nothing but win2k and 2k3 servers like fatal error and a few others. Check www.zone-h.org for that kind of stats.
But if you know IIS go for it I say, It never hurts to dive in and learn. Then if you think you cant handle it get a server management company
You should probably consider a small level of managed services initially until you get your feet wet. You should be fine just make sure you double check your work because you are now the one who can screw everything up for yourself. If you were on LInux I would be a little more worried because if you dont know what you are doing you would be lost...Windows not so much.
I'd have to agree with the rest windows is kinda forgiving. Don't be to sacred because windows isn't that hard to learn. If unsure most hosting companies will help you out with any questions you may have. And like the rest said look for a managed or semi-managed if really that worried