And if yes should I do anything before I restart, I just played the main story back then and didn't even look for what else the game has to offer and well I also caught all legends except Dialga/Palkia and Giratina and played some quite a lot battle frontier.

Note last time I played anything else in this game besides battle frontier was 2009 and I was super casual player back then, which is why I want to replay the older games.