Each person creates a squad leader who controls a company of soldiers. You have access to medieval technology and magic, and can be of any non op fantasy race (created by you or otherwise). The more powerful your individual soldiers the less of them you can have. As a standard, your company of soldiers should be equal in power to 100 average humans with average equipment; a balanced mix of bows and melee. If your people have magic powerful enough to defeat two humans then you'd only have 50 in your company to remain balanced with everyone else. The lowest amount I'll allow for a company will be 20, which can defeat the average human soldier at a 5 to 1 ratio. The highest amount I'll allow is 500, the same ratio but against you. The squad leaders can be three times as good as the rest of your generic soldiers. The battle can have multiple people joining in, each in command of their own company. You're not limited to a single team, so can betray your allies at any time and even form another team outside of the two main sides fighting (the good and evil sides). There is no leader for the entire side unless all the players on that side agree that they can be the leader for whatever reason. Maybe you plan on being abscent at some point and need someone to fight in your steed or something. Otherwise, don't act like you own the place (not to say your characters can't try to be jerks like that).
Every turn will have everyone say their actions to take place in a certain time frame, most often only a couple minutes because things can change very fast in battle. The ones attacking will have to post first. That doesn't mean your opponents can just see exactly what you're doing and counter it perfectly unless they could reasonably be expected to do so in real life. For example, if you post that you're storming the main gate across the open field, the enemy soldiers could easily see that's what your doing and counter it, so don't blame it on having to post first and the other person cheating off that. Now if you had posted about spies sneaking through some unprotected area that couldn't likely be seen from the enemy's position, yet the other person reads your post and then posts that they decided to station guards there for no reason, then you'd have a valid reason to complain and I will judge the situation accordingly. The same goes the other way if the defender places some traps somewhere, don't all of a sudden change your attack plan without a valid reason to do so. That being said, yes, more then likely at some point or another you will know something that could drastically change your situation for the better, but don't take it or else you'd be cheating if it's not expected for your characters to know as well. If you don't like that then don't join. Save everyone the trouble.
So is anyone interested in joining? Any battlefields that you'd like to have this take place in? You can suggest things like a beach, but if we later see that your race powers up near water then obviously we don't need to accept your unfair request. The attackers might have a disadvantage so their team should be able to have the final say on the location of their attack, although to help balance things out the defenders can post more of the finer details of the location.
By the way, if the first battle goes well and we decide to do more battles in the future, people who do fair play, have good sportsmanship, use a lot of clever tactics, etc. will be rewarded with heroes, larger number of units, or other benefits for the next battle. People who do the opposite will be punished in the next battle until they prove themselves. Wining the battle is not as important to rewards as how you win. (Don't worry, this doesn't mean you can't betray your allies in game or else lose points. I'm mainly talking about sportsmentship among us rather then the characters).
EDIT: Each company may get up to 3 heroes (or some other amount), and maybe reinforcements. We'll see.