Calcium with D3 is most important, especially as they are growing. Vitamins and minerals are good as well.
My adult LG's get Calcium w/D3 2X a week and a multivitamin with minerals 1X a week, but not more.
LG's can handle calcium well (you can leave calcium in a small bowl in the tank and they will eat it when they need it and it won't harm them at all) but can only process excess vitamins to an extent - especially beta carotene. Try to get good quality vitamins as the source for the beta carotene is usually better and therefore better for LG's.
Make sure you are gut-loading your food with good stuff and that's over half the battle.
In summary.
1. Gut load LG food with good quality food.
2. Calcium 2X a week for adults and 3X for young LG's. You can also leave calcium in a bowl in the tank in addition to sprinkling food and they will eat when they need it.
3. Good vitamin 1X a week.