Are my ADA locked when I Stake in the Pool?
In Cardano the Staking process don't lock your ADA and you are always able to send/spend them at any time.
Is there any risk to lose my ADA while Staking in the Pool?
There isn't any risk in the staking process. Just keep your wallet secret words and spending password safe.
Must I withdraw my rewards every Epoch?
Your rewards are auto-staked so you don't need to withdraw them unless you are going to spend/send them out
What happens if I add more ADA to mi wallet?
Every new ADA that you send to you wallet is auto-staked, so you don't need doing anything
When should I receive my rewards?
For being rewarded the Pool needs to produce blocks. The first reward always arrives between 15 and 20 days after the delegation. As of there it will come at the end of every Epoch (5 days).