I'm not the owner, but I like that app. I think its possible to just track your expenses, but its impossible to take money from "nowhere" so you have to have at least one account. In this case you'll have negative balance on that account which will be set to 0 each month.
As for "How much do you want to spend each month", its not mandatory but gives a new user an idea how to use all app features.
Its good to see article like this. Many just don't realise that drug boost usage may result in serious damage. So far the best brain booster is healthy lifestyle and practice.