It varies by location. Some places limit $1,000. Other places limit $900.
Yes, you will have to report to them how much you make. Be careful though... they are very anal about how much you make.
For instance, they tell you that your limit is $923 per month. If you make $923.01, then that's considered "over" and you will be penalized for it. When I say "penalized", I don't mean a hefty fine against you... but whatever you have worked out with them.
Where I live, they allow you to go "over" 9 times before they cut support.
Another reason why it's often risky with going close to the monthly limit is because of when we get paid.
Let's suppose you get paid every Friday. Some months have 4 Fridays and some have 5 Fridays. If you established a steady schedule weekly of $230, then you know you would be fine and not go over the $923 limit. However, one month... you happen to have a 5th Friday... which takes you over the $923 limit. Oops! The same applies to bi-weekly checks. What if you get paid the first, third, and fifth Friday? That's 3 checks instead of 2! Yikes!
So, be careful with how much you're making and how often you're working.
My best suggestion for the "better safe than sorry" approach would be to consider every month as being 5 weeks long. With that, you can take the monthly limit and divide that by 5 to determine your weekly earnings. In that case, a limit of $923 would give you a safe weekly limit of $184.
Oh, I forgot to add... some companies provide bonuses. You may not always know about it, but they reward you with a bonus depending on what you did during work. That bonus can take you over as well. Eek!