Find the minimum characters to insert to make a string a palindrome.

Focus on breaking down the problem by first understanding what a palindrome is and how it can be formed from a given string. Discuss the concept of dynamic programming as a potential solution, specifically how to create a 2D table to track the minimum insertions needed for substrings. Be prepared to explain the logic behind filling the table, including how to handle cases where characters match or do not match. Finally, articulate the time and space complexity of your approach, and consider edge cases such as empty strings or strings that are already palindromes.