I neeed to build a process to complete the following:

Read all records from an Object  (10000+ records)
Apply criteria to group the records by user and accumulate count fields
Insert the resulting records (User, Count) 

I dont believe I can use Batchable as I need to read all of the records before building the output records.
If this is possible, would I likely hit processing limits?

I was able to build this logic using a Java program and API calls, but have been asked if possible to build Salesforce job to do the same?
 

I have added a Custom Button to a list view for a Custom Object. I would like to be able to edit the selected records before processing them. So for example, the function under the Custom Button is only valid for records of a certain status. So if the user selected records that are not in the correct status, I would like to display a message on the list view screen indicating this. And also retain the user selection. Another edit may be that the function can only be completed on X number of records at a time. So if the user selected more than X, display the message on the list screen while retaining what was selected and allow the user to "update" their selection.

If the users selected records are "valid" they would get passed on to be processed.
Is something like this possible? I have tried a few things but had no luck getting a message on the list view or retaining the selected records.

Thanks in advance for any suggestions.

I have added a Custom Button to a list view for a Custom Object. I would like to be able to edit the selected records before processing them. So for example, the function under the Custom Button is only valid for records of a certain status. So if the user selected records that are not in the correct status, I would like to display a message on the list view screen indicating this. And also retain the user selection. Another edit may be that the function can only be completed on X number of records at a time. So if the user selected more than X, display the message on the list screen while retaining what was selected and allow the user to "update" their selection.

If the users selected records are "valid" they would get passed on to be processed.
Is something like this possible? I have tried a few things but had no luck getting a message on the list view or retaining the selected records.

Thanks in advance for any suggestions.