1. If you are self hosting the community edition of SigNoz, it is free of cost. There is no limit on the amount of logs - though there are some feature differences in the community edition and cloud/enterprise edition. Details
here
2. No
3. If you are self hosting SigNoz, the security depends on your cloud setup where you are hosting
4. We don't get access to your data or code, but we do get access to some data on how you are using the product - more details
here