Batching Update of records

Hello, I am going to use the NeedIt example practice/training application as an example. How would I update the NeedIt records to look up the email of each of the records for the "requested_for" user field and store the result in the "requested_for_email" in the record? So I would like to make it a scheduled script execution running every few minutes to only update the first 100 records where the email address is blank. I was thinking along the lines of setting a dirty-bit hidden field and updating only the first 100 records where that field hasn't been marked until every record has been marked as having been processed.

Or conversely, I could mark the first 100 records where the email still HASN'T been added and process THOSE records until the marking process cannot mark anymore records with a missing email address (ie all records where email field has an email address.). When it processes a record in the course of its loop, it removes that marked field.

The purpose for this is I am attempting to update records in batches to simulate having a very large database where I would need to update every record with a missing data field and don't want to lock up the system by attempting to update every record with one single script all in one go.

I used to do something like this with a SQL script but moving to ServiceNow from another platform I am attempting to learn JavaScript and the methods and syntaxes for all that. Still getting used to GlideRecords and Ajax and such, so I'm learning how to perform a somewhat complex process such as batching to pull email from a user record whose user record is from a field and all that, I just want to wrap my head around it. How to pull the email field from the "requested_for" user and put that in the "requested_for_email" field?

The pseudocode would look something like this:

Scheduled Script Run every 5 minutes

//Initialize mark first 100 records without an email
var counter = 0;
while counter <= 100; //Yes I know this can be an endless loop, I need to figure out how to break if it has gone through every record and counter is still less than 100
{
    if (NeedIt.requested_for_email == null)
    {
        NeedIt.dirtybit = true; //Mark 100 records with no Email
        counter =+ 1; //Increment counter
    }
}
//Can skip processing altogether if the counter is 0 at the end
if (counter == 0)
{return}

for each (NeedIt.dirtybit = true) //loop through database for only the marked records or just update each record marked.
{
    var emailLookup = lookup(requested_for); //look up email address for user in requested_for field
    NeedIt.requested_for_email = emailLookup; //set email into the NeedIt Record
    NeedIt.dirtybit = false; //clear dirty bit
}

I'm not entirely sure what the exact syntax for all this would look like, so taking the NeedIt application as a foundational example could someone help write it as a proper script so I can learn the syntax. There are many many different ways to do this so if you know a better method, by all means share as well!