I'll try to quote the requirements from your description and place the answer below it to make it understandable.
Given the scenario you have described, your first requirement would be:
"I would like to capture something like an OnClick event on the server side that fires immediately after the user clicks on the grid's edit image (the pencil) or insert command link. These events would fire before there is any attempt to bring up a custom edit/insert form or the default in-place form for edits/inserts."
Client events cannot be fired on the server, but you can call the Event handler manually if you wish. Although, If using the built-in Edit/Delete Columns, the right event would be the ItemCommand. This event fires before the actions are completed. You can cancel it, if you wish to do something else.
The following articles will provide you with more information about Commands and methods. You can use a combination of these methods/commands to execute further logic on the server:
"In that event, I plan to redirect to another page (X) to be used for inserting and updating. Within the event, I would need to know if the edit or insert command had been fired."
You have access to the event arguments, and there you can understand which commands was fired. Insert/Edit/Delete or even Custom. Make the redirection, or just run other logic.
"When editing, I would need to be able to get the record id so I could get all the record's data to display in the edit form."
List of articles that will help you access cells, values, controls and more in the grid items:
Example Running Sample Project with Manual CRUD operations: Update all, individual or selected rows using RadGrid with InPlace edit mode
Everything you have described can be easily achieved. Following the instructions from the links I've shared above, will help you go through and find the way to implement this. Please give it a try, and in let us know if you need further assistance.
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