There's plenty of problems with this:
First of all, in a pre-industrial, pre-gunpowder society, women in the military just does not work on a societal scale. Its just demographically unworkable (imagine if the Roman losses in the Second Punic War were divided equally among men and women; it'd be doomed). So, you could hypothetically have a society that on paper says 'yes, women can be incorporated into the military' without actually following through on it. Thats really the closest you're going to get.
This flows into the next point, that, in most governments throughout history, political power flows directly from the military. Even civil government derives its authority from force. Since the proposition directly calls for a militant expansionist empire, we're tied to that sort of society that explicitly bases itself on the martial virtues. A sex-blind military is not going to work there.
I'd like to go out of order and look at the issue of nepotism. We know that the idea of feudalism has the division of society along those who fight, pray, and work. Well, there's a reason why there's that division and why major empires tend to work with standing armies: Being a militant society generally requires a well trained military that is devoted to that vocation before all else. Look at the Spartans, who famously devoted their entire society to war, rather than agriculture, trade, or any other vocation.
Again, we can look at a feudal societies to really appreciate the challenge: You're a peasant. You have some idea of how to fight, and you might get levied in case of a war. You're little more than cannon fodder, because your skill set is growing crops and tending livestock. Your sons are going to be raised with that same skill set, as a matter of necessity (the whole having food to eat being a powerful motivator). Now, consider a noble (in the era when the nobles were actually regularly engaging in martial matters, as opposed to a Sun King style court). Your whole responsibility in life is to maintain yourself and your companions as able warriors. You've studied war from an early age, you've practiced in the courtyard of your castle, you've accompanied your older relatives on campaigns, and your son is now learning from you. This was your father's job, its your job, and it will be your son's job. You see how this sort of stratified society reinforces itself? Hell, just watch the parts of Game of Thrones that deals with Jon Snow's training on the wall; he's the only recruit who even knows how to handle a sword. Because he's a noble.
You can maintain a comparatively small city-state, even up to a medium sized power, for awhile, on the idea of a citizen army, like most of the Greek poleis and the Roman Republic. But, at a certain point, there needs to be a dedicated military, and that tends towards stratification.
And, of course, it almost needs not be said that a certain level of nepotism is just natural. If you're in a position of authority, and you need to rely on any subordinates, you're prone to want those that you know you can trust and those whose skills you know the best. That tends to be close friends and family.
Now, lets look at the issue of religion. Here, the idea of a anti-religious society (just for shorthand) can be seen as directly opposing the idea of a meritocratic society. To be sure, the clergy were often dominated by the nobility in many different societies (particularly in those societies that had hereditary priesthoods, of course), but they did tend to offer avenues of advancement outside of the idea of military skill being most important for leadership (especially, in the case of Christendom, for women).
So, what can you achieve?
If you want a hyper-meritocrat Empire, your best bet is a mercantile society, not a martial society. Heck, even in martial societies, it was often considered the responsibility of women to manage financial affairs, so their opportunities for equality in a mercantile society are much better. Further, if you want it to be less than zealous, you're in luck. Think of all the religions that tend to frown on the accumulation of wealth. Now, avoiding nepotism... thats hard. In fact, I say its impossible, long term. But, luckily, if its a truly plutocratic society, well, old fortunes tend to be lost quickly by less than merited generations.
