Hmmmm... K3WRO said his FL couldn't find Reason and neither does mine (demo, that is). This seems like a common issue. Silly FL! But demo of Reason works perfectly. I've used it along with Reaper for a good while now.
Prettiest, there shouldn't be limitations like that (unless your host says so). There are usually 16 MIDI channels but at least I seem to have 16 channels on 15 buses so that's boat load of more channels.

Still I've never managed to use even 10 channels at same time.
Worthy of pointing out about ReWire:
The DAW you work on should be
host aka
mixer. That means that you should start your host first and other DAW(s) later. Now your host tells
slave aka
synthesizer DAW(s) what is the tempo, when to start and when to stop etc.
If you want to use Reason's stuff as an effect for a synth from your host, maybe render that track and import to Reason. Of course if you use demo you'll have to do it every time you start Reason again because you can't load projects.