Still, it might be interesting in ways you'd have to trade personal participation for situational awareness - for example find a high place with good view if you want to command the battle effectively.
Though I don't think actual production (buildings, troops) would mesh well with that view.
It would be better to have separate time compressed or TB mode with ts own view to manage the infrastructure and your people, with game only going proper RT when going around and in battles.
Indeed, it would make sense in battle, and would reinforce immersion and make troops harder to command, which would even be good from a simulation point of view.
On second thought, the RTS building elements remind me of Shadowbane (maybe Darkfall too. Haven't played it) or Eve online (although Eve online replaced RPG elements), but in single player.
Anyway, if it is a completely new gaming experience, asking for our impressions about something that does not exist will yield poor results. The best way would be to get a playable prototype out ASAP, and see whether it works (that might be a bit late if the game is scheduled to launch soon), and how to refine it.
Depending on how close it is to an RTS, it might work or not at all :
RTS are completely abstract. Making a RPG with RTS elements as is would be akward (with building erected in 1 minute, how would that not break immersion? What is this strange city where people are "produced"? The idea of visiting a Age of Kings city is hardly appealing. And if you don't follow the RTS formula too closely then why insist on keeping the RTS part (I mean, if it doesn't follow the conventions of the RTS genre, then why insist on calling it an RTS, which is a genre with its conventions and not any game in real time with strategic elements).
Concerning the naming conventions, why insist on calling it an FPS when what you mean is first person action RPG? It only adds confusion (or do you intend to have the game focus be shooting arrows, with melee being an afterthough, and the RPG elements a vague pretext to reach a broader audience?)
I personnally would really like a blend of RPG and fiefdom management done well, but with the little infos given there, it is hard to be of much use.