You can use two filters, such as "Created Date greater or equal Jan 1, 2022 AND Created Date less or equal Feb 28, 2022", or you can use a relative date filter, such as "Created Date equals NEXT 2 MONTHS" or "Created Date equals THIS MONTH, NEXT MONTH".
The LastModifiedBy field only shows when the record was updated, not specific to any field. There's no way to tell definitively the last time a field was used. Usage of Field Trip or the like can determine if a field is frequently used, but not when it was last used. You will need to perform manual analysis to see if a field is worth keeping. I usually ...
We may not be able to achieve with Validation rules. You can achieve it by defining Matching rule and Duplicate rule with condition that field is not equal to NA.
Please find the below resources for Matching rule and Duplicate rules.
You could use a "quick action".
Go to Setup => Object Manager => Buttons, Links, and Actions and press "New Action"
Choose Create a Record as Action type, Target Object should be Contract and Label could be something like "New Contract".
Choose the fields required to create the Contract (to add to the layout).
Than comes ...