I would say you should hire an attorney, but that's up to you. If the first DUI was dismissed, and it should have been if you were given diversion, this should be prosecuted as your first DUI. The other one should not count against you. But that all depends how that county handled the DUI. Consult with an attorney to be sure.
You question is difficult to answer. By statute, a person cannot get a withhold on a DUI conviction. And, diversion usually is not available to people accused of DUI. A local criminal defense attorney would be able to help you sort through your record.
It's not impossible that you got diversion. Orange and Osceola Counties both have diversion for some first time DUIs. If that is the case, then the charg should have been dismissed. I agree, there is no such thing that I know of as a withhold of adjudication on a DUI.
To answer your question specifically, if adjudication was withheld, then the second time DUI penalties will apply.
If your previous DUI resulted in a dismissal because you completed a pretrial diversion program, then the first time DUI penalties will apply. And, since you live in Winter Garden, it is likely you were in Pretrial Diversion and the case was dismissed, not "withheld."
The only way you could have received a withhold was if you were sentenced as a Youthful Offender, which is highly unlikely and only applies if you had a companion felony charge.
Finally, you should get an attorney. Even if your previous case was dismissed, the State will seek second time penalties. And you may have a very good defense and still be able to avoid a conviction. Hiring an attorney is an investment in your future.