As you said, you completed some free plat offers, i would definitely spend that plat on buying character slots and then take daily blessings every day...once any of your chars gets 3x combo elixir, use it to level up...the more chars you have, the bigger is your chance for such an elixir and with 24h of 3x combo elixir you can do a lot hehe...at least that´s the way i am doing this, all the best