Would a fantasy RP which involved society construction be okay? MxF only, if that's fine with you. I am over 18, by the way.

I am open to ideas myself, but here's an idea which I have so far. I'd be happy to incorporate ideas from the ideas you have pitched in # 1-4 which you have posted above.

The orcish realm of Marzala is built on the strength of its armies. Constantly at war with the surrounding human kingdoms, Marzala has only survived through constant military preparedness. It's capital, Blackspire, is as a much a fortress as a city. The orcs themselves still live in regions which are ruled by counts and dukes, but these titles and their associated regions are simply the old areas once ruled by migratory tribes. A few generations ago, a great orcish chief united the tribes and built a large camp at the base of Mount Blackspire. Since then, the titles of "chief" and "chieftain" have given way to human-sounding ranks adopted from the surrounding realms.

In this war-torn era, the military of Marzala has gained social primacy. While orcs were always warlike, this was usually limited to raids and campaigns for part of a year, not a full-time standing army. Soldiers and officers have gained power at the expense of the rest of society, including civilians and females, the latter of which are only rarely allowed to fight (only if they have magic, a path open to males and females alike). Part of this is due to adherence to old-fashioned tradition, but part of it is due to the danger of losing the ability to replace losses in battle. Male orcs can take on as many wives as they can attract and support, usually both can be accomplished by bringing back plunder from war and developing a reputation for prowess in battle. 

While a large part of the male population was off at war, the females were left behind to run the homesteads, look after the children, and even take part in a few traditionally-male roles such as hunting. Social expectations between the sexes have led to differences in lifestyles; female orcs generally dress more like their old counterparts, usually lacking footwear and never using armor. Male orcs are encouraged to dress in heavier and more elaborate garments as a way of showing off their wealth, and they use the heaviest armor possible in battle. The relatively equal status males and females once had was long lost; males are expected to fight, females to breed. While most males are okay with it, many females chafe at the restrictions, though they rarely speak of it in public.    

Then, one of the most destabilizing things possible to Marzala happened: peace broke out. An entire generation of male orcs was left with little to do, with little chance for glory and even less of proving themselves to attract a mate. Apart from a few petty border skirmishes, there is no more warfare; the human kingdoms have formed an alliance so powerful that Marzala's king will not dare defy it. To give his warriors an outlet, the king has constructed a mighty arena in Blackspire, a place where only the strong will survive and a lucky few will find the glory and fortune they seek. Most of these fights are with weapons and end in the death of one or both combatants, but a few contests are nonlethal fistfights, usually to satisfy those orcs who wish to compete for lesser prizes without running the risk of dying for them. A rare treat for the crowd these days is a fight between an orchish gladiator and a captured human caught on patrol or in a border skirmish.

Recently, one of the King's daughters has entered the fray as a fighter, going up against opponents in the nonlethal bouts. At the same time, a human soldier has been captured, the sole survivor of his patrol. He is destined for the arena, although he has no intention of dying there. At the same time, the orc princess is tired of the same old fights, bouts she wins about half the time. The two characters find themselves on a collision course, a deadly adventure where anything can happen.

And even if nothing comes of this idea here, I might be able to reuse it (or elements of it) for another RP with someone else. Maybe the human could come from the land of Eleon?