Model: 1 to 3 dwarven Journeymen as one unit
Skill 1: Build Cannon Tower (50 mana)
The spell has 5 charges. For each charge, the JM can construct one Mini-Cannon Tower with (?-?-?-?) HP in front of him that acts like a totem and shoots at nearby enemies for (?-?-?-?) damage. After activating the spell, the tower has to built for (2-1.5-1-0.5) seconds on it's own before it can attack and another one can be built. By right-clicking on a tower, the JM de-constructs the tower in the same time as above and regains a charge and (20-30-40-50) mana. If a tower is destroyed by the enemy, the charge is lost. Charges are individual for each JM unit, so you can have 15 towers at the same time.
Skill 2: Build Garrison (125 mana)
The JM constructs a Mini-Garrison in front of him. While near a Garrison, the JM regains a Cannon Tower charge every (5-4-3-2) seconds and a Swarm out! charge every (12-10-7-5) seconds. It also provides (?-?-?-?) HP and (?-?-?-?) Mana regeneration to the JM. The Garrison has 1 hp and gives a high bounty when killed. It can be destroyed by the JM himself to deny the enemy. Only 1 Garrison at a time can be active. High cooldown.
Skill 3: Swarm out! (75 mana)
The spell has 2 charges. For every charge, the JM can create a duplication of himself, for a max of 3 units at the same time. This is represented by the number of Journeymen in the model. A unit with 2 charges will have 3 JM as his model, if he activates this skill, there will be one unit with a 2 JM model/1 charge and one with a 1 JM model/0 charge, if he activates the skill again, there will be 3 units with 1 JM as a model and no charges. If a unit is killed, there will be no XP or gold reward. The Journeyman dies and gives XP/Gold if the last unit dies. The JM himself only gains xp if all of his units are in range of the xp source. Items are duplicated for every unit and can only be added to inventory/dropped/picked up if the JM is a single unit.
2-model units have (66-69-72-75)% HP and damage, 1-model units have (33-37-43-50)% HP/damage.
Subskill 3: Stand united! (No mana)
The current unit moves to the nearest JM unit and combines with it. The charges used are restored.
Skill 4: Almighty Commander (150 mana)
The Enemy is slowed for (5-6.5-8) seconds for (30-40-50)%.
In a 400 radius around the target, all enemies suffer -5 armor.
In a 500 radius around the casting JM unit, all allies gain 5 armor.
Shared cooldown across all JM units.
Playstyle: In early/mid-game, he is used to effectively push a lane with his towers or provide clutch defense by teleporting and quickly dropping 15 towers to stop a push from overrunning a base tower until other help arrives. He can also disregard the towers in favor of harassing the enemy heroes with his split off units which can be replaced at the Garrison after a creep wave. In mid/end-game he is heavily item-effect dependant, and utilizes the 3 units to deal large amounts of damage with chain lightning, manaburn, or stun morph-attacks, or provide support with cyclone/hex items. He can also set up tower traps to cut off escape-routes or scouting towers to prevent getting flanked. His survivability comes from the Swarm out! skill, as he won't die as long as one unit makes it out, which also makes him good as an initiator, as he can simply walk/blink two units in to eat the damage while keeping one in safety.
Notes on Cannon Tower/Garrison:
The tower damage/hp has to be balanced by the fact that the JM needs to get at least 1 level of Garrison and Swarm out! to place 15 towers effectively. They should have enough damage to make low level heroes not walk into a farm as much as they don't want to walk into a normal tower. For scaling purposes, it might be good to make the towers deal a % of the max health of the target as damage, so they are still viable endgame (1-1.33% per hit?) . They need enough hp to survive stray AE damage, but not a determined assault of 2-3 spells of the appropriate levels. I'd say, an equal level Pyro should need a wave + 1 auto attack hit to kill a tower. If the towers turn out to be useless/one-dimensional, the skill could be split up into Arrow/Cannon/Shield tower. Arrow only damages creeps, Cannon only heroes, Shield protects all other towers and allied structures and need to be killed first.
Garrison should serve as a fallback point for the JM that has to be placed in safety, and has to be killed by enemy heroes if they want to get rid of the JM in their lane. The regen shouldn't replace a fountain visit when heavily damaged, but should allow the JM to get back into action when he is finished restocking his charges, mana-wise.
Further balance issues:
Having 3 fully functional units might be imbalanced when combined with some items, for example direct damage (dagon?) or +armor items who can negate the hp loss by the split by adding damage reduction instead.
15 Towers might be too much, as you can spread them out to avoid AE, creating an unbreakable line of death.
The JM might be simply unkillable with blink/Post Haste.