I definitely agree with making the Erebor scout hero Dori/Nori. As for Rivendell, there is 1 thing nobody seems to have questioned yet, what would happen if Elrond ended up with the Ring? With that influence constantly nearby gnawing away at Bilbo's mind, bad things might happen. It could be a system similar to Lothlorien, where he can only be recruited once Elrond has the Ring, and then Elrond could give it to Bilbo or Bilbo maybe would steal it from him, something along these lines.
For example, you could synergize his hunger for knowledge in the library with some unique Ring hero powers, that make the spellbook powers recharge insanely fast, like 75% faster. Or you could make him give a global recharge time bonus to all ability timers on all units. With this method, he wouldn't be a very powerful fighter in his own right, but would still stack up in terms of the damage you could inflict due to all your units getting improved abilities with faster recharge times. That's my idea for him anyways.