I’m not sure I understand what you mean in the first part. How is the folder created, and what does the workflow do?
The value in the field _vLookupID is automatically created by the vLookup script when a new item is created, so I’m not sure this can be used to “know” if a folder has been created. It would be better to write to another field when whatever code / wf that created the folder has finished.
When it comes to the performance part, it will affect the loading of the form – especially if you query a large dataset, or have multiple vLookups on the first tab.
To minimize the loading time, you should put the vLookup columns in a separate tab as they are not loaded before the field is made visible in a tab.
Alexander