I think you can get 200 and be safe. The biggest concern I would have would be the previous maintenance record. The Zetec will hold 14psi of boost at which point things start to break. So You could run 10psi of boost safely, which will net you about 100hp gains. Personally, I think 10psi is still a bit much to be running all the time, but thats just my opinion. I would personally feel better about running 7-8.
If you do not to a turbo kit, get yourself a SVT header conversion. It nets you about 15-20hp gains just by bolting it on. It can be a little pricey for everything you need for this, but search on the forums for the topic and it will give you all of the details. You could combine this with the OBX exhaust system, for a nice free flowing exhaust with a nice tone to it.
You can also look into intake systems such as cold air intake, or short ram intake. I prefer the cold air intake due to the fact it doesnt suck hot air from the engine compartment back into the motor. Other people feel different about this. To each their own, and its your car, so you can decide which way you want to go. My advice for a cold air intake (if you go this route) is to make sure you get a Bypass Valve. It basically acts as an inline air filter should the main filter get submerged in water. Helps save the motor.
A throttle body will give you better throttle response, but it doesnt really net any hp gains, if any at all. Personal preference here if you want the "peppier", more responsive throttle. 65mm is the way to go. Personally I like mine, but I only did this bc my factory TB went bad. Not a bad mod, but can be a little pricey.
Above all, if you do any mods, I recomment you get a hold of Tom, 1turbofocus(his username on this forum) for a tune. A little pricey, but it will help you to get the most out of any mods you do.
Hope I helped in someway, and that if I missed something, that others can chime in as well. Also, Welcome to the forum.
00 ZX3 ATX. Sportlines, Strut Bar, 65mm TB, 4-1 Header 2.5/3" exhaust
03 SE Zetec/MTX75 swapped. Stock
Hatch Nation #31