Is it realistic to expect to earn 100 onions in a week or two using the onion forum?
I won't say it's impossible, but just a challenge.
without trying, you can never know!!
I suggest what you can do or what I would do is, work on your DeepOnions thru your Deepoints activity in DeepOnion.org. while working on it, buy some using your spare money. let's say you were able to manage to buy 50 Onions, by the time you did that, by working on your Deepoints where you get DeepOnions as reward, you'll be able to complete your first 100 DeepOnions. Because the goal is to do that as soon as possible.