Don't worry about that if you don't want to. There are always carry overs from past games to the next one but it's not really exclusive. You can get that stuff later on, it just makes for some free stuff early on. If you're lower than level 70 you get 100 of every sepith, an Attack 1, and a Zeram Powder. 70-79 is 300 of every sepith, Soul Blur and everything else is the same, and at level 80 is 500 sepith and Saintly Force on top of everything else. It's just a question of if you want to get those for early on because you'll get them later in the game regardless.
Also, Rean's level will carry over up to level 80