Do I need a Financial Planner? Do I need someone to manage my investments?
Maybe not. Some people are able to do these things on their own. You have to ask yourself 3 big questions, and if you can't answer yes to all of them, I would suggest you should utilize a financial planner.
Do you have the time? Given that, because yours will be the only case you are working on, you will be far less efficient than an experienced advisor who has gone beyond the 10,000 hours of work in the field needed for mastery. (see "Outliers" by Malcolm Gladwell https://www.sparknotes.com/lit/outliers/summary/)
Do you have the skill, the training, to evaluate the thousands of options before you? To keep up to date on the laws and regulations? To utilize the available software?
Do you have the interest to stay current for decades and the temperament to remain dispassionate and logical, to forego the input of an outsider who has no emotional attachment to whether you were right or wrong in the past?