I think the best way to go about using Allomancy would be to use a 'flare' system - all basic Allomantic skills would be free (i.e slightly enhanced strengt h - Pewter, small-medium steelpushes and ironpulls, slightly enhanced sight and hearing) but to perform special moves would require 'flares' which could be replenished using a metal vial.
For Example
Pewter - Basic Skills: Enhanced Kicks, Punches etc, Enhanced Speed and Agility, Enhanced Reactions (Ability to
counter enemies moves)
Advanced Skills: Health Regeneration, Temporary immunity to damage, 'Super Moves' e.g. Ground Pound, 1 hit KO
Tin - Basic Skills: Zooming in on enemies, Ability to hear/see/smell enemies nearby (takes the form of a minimap)
Advanced Skills: Ability to temporarily tell if characters on minimap are friends, enemies etc, Ability to shock
yourself out of being KO'ed
Iron - Basic Skills: Ability to pull on small metal objects and anyone wearing metal (most enemies excluding
Allomancers/Inquisitors/Hazekillers), Ability to pull yourself towards large sources of metal at
some speed
Advanced Skills: Pulling large metal objects, 'Super Moves'
Steel - Basic Skills: Ability to push on metal objects and , Ability to shoot coins, Ability to Steeljump small
heights
Advanced Skills: Ability to perform massive Steeljumps, Ability to Steelpush large objects
Brass - Basic Skills: Ability to soothe peoples emotions during conversations
Advanced Skills: Ability to calm the suspicions of nearby enemies (excluding Allomancers/Inquisitors and
possibly Hazekillers), (Possible) Ability to put enemies to sleep and therefore avoid
fighting them
Zinc - Basic Skills: Ability to riot someone's emotions during converations
Advanced Skills: Ability to riot nearby enemies fears in an attempt to get them to to run away or attack each
other
Copper - Basic Skills: Hides you from other Allomancers (excluding Inquisitors)
Advanced Skills: Temporarily confuses Inquisitors (situational)
Bronze - Basic Skills: None (Copper renders this redundant)
Advanced Skills: Allows you to detect nearby Allomancers on the minimap
Atium - When activated enters you into 'Atium mode'. Whilst in 'Atium mode' time will seem to slow down, every attack
will be on target and your character will be able to counter automatically. That said Atium vials will be rare
and worth large sums of money. Possible drops from enemy Mistborn?
And possibly for later games
Duralumin - When used in conjunction with other metals allows to use 'Ultra moves' (not necessarily called that in-
game) which will have devastating effects but instantly alert any nearby Allomancers to your presence.
Note by advanced skills I don't mean that they're acquired any earlier in-game just that they require 'flares' to use