Okay well first of all welcome to the teenage keepers club
100l you'll find is a nice step up from the small tank you have now. Live plants are always awsome to have, suggested easy to keep plants would be, Java Fern/moss, Ambulia, Cabomba, Indian Fern and Water Sprite.
What Wattage heater do you have in your little tank? i would suggest a minimum 100watt heater for your new tank. Also filtration, you'll want a powerhead filter of some kind with an LPH of 300-500, Suggestion a Shark400 or Shark600, there great filters.
As for stocking, at the end of the day its up to you, best to keep a beginners tanks slightly less stocked. Bascially in your tank i would suggest 20inches of fish, so figure out the fish sizes, and work from there on how many fish you can keep in your tank.
Shae