Hi Rubab,
Is the release immediately flag is set at preventive Maintenance Order type ? If you dont want to release immediately, uncheck it.
One of my client is using User Status for different levels of approvals so, they dont want to get the order released immediately.
Answer to your 2 nd question, It depends how you are going to code, if the release strategy falls only for release not based on adding components, then there is no issues.
SAP Standard functionality allows to add materials after release also.
Regards
Terence