Hot digity damn!
Gon' buy this once it's available that's for sure.
I have just spent the last few days enthralled by Battle Brothers. Please do yourself a huge favor, and play it.
It has ideas I think you could use, and seems in a similar vein as to what you are doing.
That map concept you have? If the entire game was in that art style I would be one happy gamer.
I very much love the low-poly look. If you aim to end up closer to the battlescene graphics, that will be fine too.
However a more realistic style tends to require a much higher level of quality in the models, textures, and rendering to pull off safely.
I hope you model permanent damage to characters, like in Dwarf Fortress. From what I am seeing of this, and Sol Trader, I am expecting essentially DF Adventure Mode. Which is very much not a bad thing, but long term damage and debilitation is a crucial part of games like DF or Battle Brothers. Forcing you to take on new allies as they slowly get ground down in combat.
If you aren't already going that way, I highly recommend low fantasy, keep magic rare as hell. This gives you something to hold in reserve for big-bads, legendary equipment, and late game things. If everyone and his dog is a wizard, then remember, humans are lazy so magic is going to power a ton of stuff. Wizard powered airships and city power-grids fed by magic are going to be things in a faithful high fantasy setting.
If you don't play Crusader Kings 2, it's time to. It has a great grasp of the more political side of things in a medieval setting. Make sure counts are attempting to marry daughters off to the sons of kings or dukes, assassination attempts are against rivals, and those who hold titles that the person attempting has claim to (or his children do).
Social Justice Warriors might get on your case if you are relatively faithful to the politics of a medieval society. But I highly recommend that you are faithful to those politics, religious and gender equality issues help drive the narrative, and give different play styles to characters born a different gender.
Beating the game easily and want a handicap? Try being a female in a world ruled by men. Games such as Mount&Blade and CK2 take this into account, although M&B doesn't go as historical as it should in my opinion.
It looks like you have a strong starting point. Sol Trader will certainly give you a massive advantage with the courtly intrigue. The social dynamic of a game like this will be fantastic.
If you get the art style right, and nail combat mechanics (seriously check out Battle Brothers for inspiration on both). Then combined with the social simulations, you will have a much less niche game than Sol Traders, with a much bigger audience.
And I for one look forward to it!
Keep up the great work.
PS. I love your Revelation Games logo.