1. Thanks for reaching out to us. In the past, customers have found using a third party performance monitor in the environment has allowed them to pinpoint the cause of the System out of memory timeouts. I had suggested previously that you try applying the latest hotfix to the instance, as a few performance upgrades were made to the application over the various releases. Have you applied the latest hotfix? Have you checked the IIS idle timeout and tried increasing it, or if there is a memory threshold in IIS that can be increased?
2. As for the object null reference, what is happening at the time of the null reference exception? It is a very general .Net error that simply means a value is set to null in a codefile, which makes it very difficult to troubleshoot without knowing when it is being thrown. Is there any custom code, (event handlers, macros, or transformations) that could be causing the exception? At the bottom of the null reference error below stack trace, it should identify a file where the exception is being thrown, which may be helpful for debugging.
3. I am not sure what you mean when you say: is the content not saving when you press save, or do you not want it to show on the live site?