Should there be laser turrets, torpedo turrets, special turrets? Should each races' turrets do different amounts of damage?

I don't know if there'll be such variety, but one of their main purposes will be anti-air defense

good point, i suppose that most turrets could fire at air and ground.

Hmm, i bet that there will be a variety of defense towers. I think that there should be: Anti-Personel turrets, Anti-Mech turrets, and Anti-Air turrets. All should be seperate, it would be too easy if they could do it all, you could just load your base with one type of tower.

maybe some races will have combined turrets, and others willhave separate like on starcraft?

my main guess is there'll be two separate turrets. Looks at what the rebels had on Hoth; they had a ground-unit-turret.
We know there's anti-air-turrets (TF has them for sure), so that leads me to believe every civ can build both anti-air and anti-ground ones. The anti-ground turrets would be particularly effective against mechs.

if this is anything like age2 the ground turrets will own infantry. Another type of turret would own mech (bombard tower).

I think 3 would be good laser early in game for troops and small mechs then rockets like the bombard tower more for mechs and third missiles for air only.