Why I'm asking:
Scenario where you try to control a group of ponies from converting humans to ponies aka. The Conversion Bureau and you're the anti-conversion commander.

> is multiple micro-scenarios in scenario possible with Traits?

Don't really know what you mean by "multiple micro-scenarios"

> can you control infected count?

Yes, events can infect, uninfect, or kill people at will.

> is it possible to create a scenario that makes PI:E look like a Proffesional Scenario Simulator?

Huh?

> will the game break if you make too much Events?

I'm working on a scenario that has 500+ events. No problems so far; it seems to be quite well-optimized.

> Is it also possible to create custom traits(traits doesn't do anything just activates an event?)

Yes, an event can specify trait dependencies (i.e. event fires when trait is evolved). So the event can do stuff while the trait itself does nothing.

Ok, since you didn't get my first question, here is a scenario.

You have regular PI:E gameplay, until the traits split off.
With the Events, choosing path one will make you stop making path two, making an entirely different scenario and vise versa.

You can't control the availability of traits with events -- you can't make it so that one set of traits disappears when another trait is evolved. Be nice to be able to do that, but it's not possible.

But you could split it into three -- transmissions is one story, symptoms is another, abilities is a third. Then make it so that trying to evolve from more than one group is an instant lose.

Or you could make it so that traits do nothing except trigger events, then the events can do different things depending on the combination (e.g. so that trait B triggers an event that does something different (or nothing at all) if trait A is also evolved).