Are there any extra costs associated with removing or adding liquidity?
Aside from the initial gas or transaction fees, which are very low on Starknet, there are no other fees for adding or taking away liquidity. To get people to take part, liquidity providers get 0.20% of the 0.3% trading fee as a fee. They can also use their LP tokens to take part in other StarkDefi offerings and earn more rewards.
Are there any deposit limits, i.e. how much users can deposit into the pools?
There are no enforced limits on the amount deposited into the pools. However, note that the greater the deposit amount, the greater the chances of winning; users that deposit larger amounts into the pool have a much higher chance of being selected for rewards.