Hi Pranay,
For validation, you can add validations on your entity so when the import is being done the database will validate the data. This will limit you to only what the database can validate.
Another option would to import the data to a non-persistent table and then do the validation in a microflow, and once the data is validated create the records that you want and commit them to the database. The second option gives you more flexibility for validating your data. Also to do this, I you would need to use the input object configuration, and then you can retrieve your data over the association of the input object.
Regarding limiting the amount of records being imported, I don't think the excel importer can do that out of the box.
Hope this helps!