Minimum level: None. But I would recommend trying to get a couple in before Sunday.
corruptors vs defenders: defenders will have better support stats in general. Incase of ELec Affinity, you would providing a better buff. Your damage output would be on the lower end. So if you solo to catch up, it could take some time.
corruptors will do more damage, and their ability to do double damage on foes with less then 50% health will be nice. Thus making solo play easier. Their support stats will be lower compared to defender. Not by a lot to break the game, mind you. So the question is: what do you prioritize?
primary/secondary: one of the sets must be electric. So if you role a scrapper/brute: elec melee/will power is approved. Elec/ice armor is approved. Ice melee/elec armor is approved. Radiation / elec armor is approved. Elec/elec is approved. Fire/will power would NOT be approved. Similarly with a corruptors: elec/**, **\Elec Afin, elec/elec are approved.
In my case: I did a elec/elec controller more so for character concept. But we have a dark miasma/ elec defender, an elec/traps troller, and an elec armor/stone melee brute as other examples.
