Find out if 25 is available in your area. If it is then you can get it. As for you wanting 3HD/1SD, your "Rodem"(see what I did there?) will always have dedicated bandwidth for your TV's. The difference between the two is pretty much splitting whatever speed your internet is advertised and then the rest goes into TV. Optik TV runs on a protocol called IPTV which works very similar to how you connect via to the internet, broadband.
The short answer is YES. If you can get get 25 in your area, you can run your TV network however you like.
Note that you will impact your internet speeds if you are streaming 3+ more TV's. Keep in mind that you have to have all 3 streaming at once to see very little difference in your internet connection. I think on the forums I've seen like a drop of 2-3mbits which is nothing.
Hope that helps. Good luck with your upgrade.