If you want a large single antenna that covers both VHF-high and UHF, the Antennacraft HBU series is often recommended.
http://www.antennacraft.net/Antennas/AntennasHBU.html
If you keep the antenna low, or you have issues with obstructions or trees in the way, you'll need to go big. At 50' you should be able to get all the OKC stations with a modest antenna like the RCA ANT751 ... but I expect the ANT751 will be too weak at 25'. I would skip the rotator - just point directly at OKC 290 magnetic. If you can go high and want to try for Tulsa stations, aim your OKC antenna there and see what you get. Then if you want to add Tulsa capability and you think it's worth it, set up another antenna and tuner, or an A/B switch, and add the additional stations. If you go high enough, the OKC stations will be strong enough that you'll probably get many of them anyway, even if you are aiming at Tulsa.
Yes, you can connect two antennas on the same coax, but they need to be different bands. The combination recommended above could be combined using a UVSJ or preamp -
http://www.solidsignal.com/pview.asp?p=uvsj
http://www.amazon.com/RCA-TVPRAMP1R-.../dp/B003P92D9Y
The UVSJ or preamp will filter out the UHF from the VHF antenna and vice-versa, and then combine the signals. No problem.
The DB8e recommended above is an excellent antenna for UHF only, and you can combine it with an Antennacraft cut-to-band antenna Y5713 or Y10713 and that combination should outperform the HBU55. But if you want a large single antenna, Antennacraft is good, or Winegard or Channelmaster (don't know the specific models - just compare the spec sheet for the big HBU antennas to their offerings).
If I were going to guy wire, I'd go with a telescoping mast, not a tower. You can get close to 50' with a telescoping mast. Look here as an example -
http://www.antennapartsoutlet.com/ I'd think you could easily extend another 5' above the last guy ring. Or sink a pipe in the ground or in a pad and put the mast on that to get a little more height.