Your staked ADA never leaves the wallet you are delegating from. Therefore, there is no risks assocated with staking.
When the pool produces blocks in an epoch, you receive rewards 10 days later. Rewards are added to your wallet automatically. If you stake with a larger pool you can expect smaller but more frequent rewards, and with a smaller pool rewards are typically larger but less frequent. In both cases, you can expect an overall annual ROA of 5%-6%.
A small transaction fee (roughly 0.17 ADA) is needed to process your staking request. An additional 2 ADA deposit is required and will be returned to you when you stop staking.
Currently the minimum you can stake is 10 ADA. Rewards are shared proportionately amongst pool delegators, so the more you stake the greater your rewards will be.
Yes, you can switch staking pools any time. The delegation snapshot is epoch-based. So if you change your staking pool halfway through an epoch, your change will take effect at the next epoch.