A quick answer:

It depends on the strain. There are seriously easily a couple hundred thousand different kinds. Anyone with a functioning brain can cross any 2 different kinds of cannabis to create a new one. You could take White Widow and cross it with Blueberry, and call it Blue Widow. Some strains yeild a lot while some don't yeild as much.

Depends on the soil. Soil makes a huge difference as it is one of the main sources of food for the plant. You have bad soil, results will be weaker, which can result in low potency and lower yeilds.

Depends on the fertilizer you use. There is a huge variety of different kinds. If you use a kind that cannabis doesn't thrive on, then again, potency and yeilds will be lower. Fert. is the other main source of food.

Depends on the conditions. When things get too hot, the plant can stretch giving you loose, light wispy buds. When things get too cold, the growing pattern slows down and the plant can turn purple as a sign of stress. If it's too wet, lower leaves can yellow and die off from getting no air and basically drowning the roots below. Too dry, it can shrivel up losing important fan leaves that the plant uses when flowering time comes.

Lastly, general care. Overwatering, overfeeding, not watering enough, removing much needed leaves and etc can have a huge impact on the end result.

Basically, the question you are asking is impossible to answer.

If you know the strain of seed you are growing, post it and some basic info can be found. There are tons of strain guides out there that give you the yeild info. height and suggested growing conditions, in pretty much perfect conditions, so you know the best care for the strain, and an idea on what to expect.

Ants shouldn't be a problem, but just keep an eye on your leaves, and if they are crawling on your plant(s), then you might want to consider finding the proper ant killer that won't harm your plant.

I'm pretty sure they don't bother with plants though as I've never had a problem with it.