EMSA is encrypted, you won't be hearing them at all.
OKC fire is using Provoice, which no scanner can decode, so won't hear them either. (There is an online feed for them, though.)
OKC police are using Provoice, but they are patched to the state system so the OHP can listen / interop with them. You can listen to them there.
OHP and many of the communities down the east side of the metro (Norman, Moore, MWC, Nichols Hills, Village, Edmond...) are on the state system.
Several communities on the west side of the metro are moving to OKC's Provoice system. Bethany and Yukon have already gone there, at least Warr Acres and Mustang have plans. Once on Provoice, you won't be able to hear them. (Again, except maybe with an online feed.)
Most county sheriffs are still on their own analog freqs, but Cleveland County is on the state system. IIRC, OK Co has allocations on the state system but don't use it as primary yet. (Haven't listened to them in a while.)
Not sure about your scanner, but Radio Shack as the PRO-164 that is a nice analog trunking scanner. Works great with the state system, and is pretty cheap right now. If you want to "future proof", you'd want to get a digital scanner in case things go P25 digital. Of course, anyone going P25 could also opt for encrypted which means even the digital scanners wouldn't hear them!
One side advantage of getting the digital scanners, though, is if what you want to listen to is primarily on the trunked systems, it is a lot easier (in my opinion) to program and work with the talkgroups on the newer scanners. I have the Radio Shack PRO-106 (handheld) and PRO-197 (base/mobile). The older scanners (including the PRO-164) are frequency-focused. You enter the frequencies for the trunking system into the banks on the scanner, then you enter talkgroup IDs into a sub-bank. You don't get as much room for TGIDs, and it's harder to manipulate them while listening (lockout, unlock, etc.) - in my opinion. With the 106/197, the focus is on the talkgroups, and you reference the talkgroups to a trunking system (that you only enter once) then the TGIDs are what you enter into scanlists (formerly banks) and directly manipulate while scanning.
But the digital scanners are a fair bit more expensive, too!