You might not NEED a strong dose regardless of how severe your depression is, it all depends on how your body metabolizes it.
As for side effects, there are many and varying side effects depending on the type of medication.
If you are really concerned about weight gain, wellbutrin and viibryd seem to be less likely to cause weight gain.
Best thing you can do is talk to your doctor/pdoc and see what they want to give you and ask them about side effects and stuff.