If individual mercs are allowed(though some of this is possible anyway):and so far archer has said no:
So long as it is not hard coded that you can have only 3 types of soldiers in a faction there should be a 4th class, the mercenary. His skills would be average in every way but would be able to purchase a very wide variety of equipment from all classes ranged/melee/cavalry. So provided the mercenary had enough money he would be able, unlike a regular soldier to wear and use almost anything he wants. They would be the most individual soldiers on the field and able to fill whatever role they choose(I think quite a nice perk). This would mean you have to tie in the in game money to the mercenaries bank account,unless they buy the weapon out of game but this would be much harder to verify. If it is hard coded no more than 3 there would be ways to work around it.
***Specific equipment and skills by the same standards would be impossible. Each mercenary would have to have his own troop file. With a sizeable force of individual mercs I have no idea if that many different troop types could even be supported. Mercenary bands would have to work differently though having their own troops like a faction, if the 4th class is available though then they could use that as well in their armies.***
-Hire your own soldiers. Bored of going around on your own from battle to battle with no mates? Got a lot of money? Buy some friends and start your own mercenary band. Or maybe you have a couple mates and want to pool your money to buy some men, lead together. Well now you have just progessed from lone merc to mercenary band. You will work just like a clan in the game would but you will have no fiefs and so no steady income other than from battles. I wonder if you will ever do anything about that...
-Mercenaries are not just goin to fill common soldier roles though are they? If some ultimate badass commander comes along playing this game as a mercenary you think the clans are just gonna sit by while he is wasted in the field? Well if I was king I might consider giving someone like that a higher role than arrow fodder. Getting hired as a commander is something to work for.
-Maybe after a good fight the faction you fought with will want to take you into their clan whether only for the purposes of the game or officially who knows. Give up your status as a merc and become a normal soldier.
So you see every mercenary if he plays the game well enough has literally everything to play for.
Once the game has started and the territories have been doled out new clans probably wont be able to move straight in as kingdoms if they want to play. They will have to play the role of mercenary bands or vassals. Who knows how far they will climb.
However personally as I said I think we ought try a much simpler version first without mercenaries at all, clans only. Mercenaries add a lot to the game, maybe too much for a first try IMO.
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-If new castles were introduced they should not be new plots of land simply upgrades of existing ones. Maybe your clan has a custom castle map they wanna use. The game admins can assess it and decide on a price. Your clan pays the gold, a week or two later your allowed to use that castle.
-Perma death should not happen. If you die you will appear a week later or something back at base and with equipment penalties though this is not the common soldiers concern only if your a merc will it matter and gold loss also if your a merc, lord level players however will be capturable, ransomable, tradeable, luckily for them also escapeable. I hope

They get whatever equipment they want though so it does not matter so much for them. Except of course limitations will have to be imposed on what they can do in the game and so restrict the clans progress.
-Personally to limit size of troops rather than limit the number of lords you should only allow a certain % of your army to be made up of AI soldiers. This % would have to be found out by playtesting(if there should be a limit at all, personally I think the best limit would be the price in gold they need for wages). You should be allowed as many lords as you want, though you may not have enough soldiers to spread them around. If clans want to stop the big factions winning then they need to work together and maybe hire some mercenaries.
-If experience was ever introduced it would apply to the army not the troops I think. Or maybe the commander, or maybe both. Either way as Archer has said experience is a thing to be added later. As are many suggestions. It is far more important to actually create a bare bones version than endlessly dream about all the possibilities, however fun
