1)Solving those selected good quality problems from leetcode and geeksforgeeks is a very good thing to do to prepare for FAANG interviews .
2)My suggestion would be , in free time , you should try codeforces , as they improve one's logic building and thinking skills in leaps and bounds . That increases your confidence , and you wont be afraid to face a question in an interview which you have never seen before !
3)Also , having a good rating on these platforms add a huge weightage to your resume and good impression on interviewer too !
Edit : 450 DSA is a pretty good list of problems for linked list,binary search tree,etc. But its not enugh for string, array and dp questions :-) In array, you need to cover a vast range of tricks and concepts compared to other coding topics for interviews.