Regarding the peasant and the laborer, you're intending one to be the gatherer and the other to be the builder, correct? In that case, you would have to make both units cheaper than a regular worker unit, since they're not capable of doing as much, so instead of having (for example) four workers gathering resources and two doing construction, you could have perhaps six peasants gathering resources and three laborers doing construction for the same cost. On the other hand, if you made peasants and laborers cost the same as regular workers, then the faction loses flexibility. They wouldn't be able to suddenly divert their units from mining gold to have them repair a damaged building or anything of that nature. If you ask me, it seems like it would be hard to balance and would most likely be more trouble than it's worth.
An alternative would be to have two units gather different resources. For example, in Warcraft 3, the Scourge's worker unit constructs/repairs buildings and mines gold while their ghouls (undead light infantry) gather lumber. There is also a mercenary unit available called a shredder which is basically like a battle machine with buzz saws that it uses to either kill people or chop down massive amounts of wood.
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http://www.battle.net/war3/images/neutr ... redder.gif)
You could have a peasant who builds buildings, repairs them, mines gold, and quarries stone, and if you wanted to give your faction more of a clockwork feel to it (which would be good for differentiating them from original Tech), you could have your lumber gathering unit be a clockwork automaton like a scaled-down version of the goblin's shredder (but without a driver), sawing down trees and serving as a mechanical infantry unit. That would also be good for separating the roles of your infantry units. The swordsman could be replaced by the slow and tough mechanical buzzsaw man, while the maceman could become a fast and lightly-armored but heavy-hitting unit, like the macemen in Lords of the Realm 2 or Stronghold. Of course the sentry would also become mechanical since he's just an upgrade of the swordsman. Call him a "watchman" if you're feeling up for a pun.
Also, I'd change the archer and longbowman to a crossbowman and an arbalist. The mechanical aspects of a crossbow make them much more appropriate in my opinion.
Fun fact: A knight, trained from a young age and outfitted in the best armor available, could be killed by a single lucky shot from an untrained peasant with a crossbow. This led Pope Innocent II to issue a ban on the use of this weapon, but it was largely ignored and the crossbow continued to be used.
