There are several key purchases on this game. For those of us who were already a bit advanced, the $4.99 packs were a good buy for converting the shards for the shard store (a feature you will learn about later on). At your level the $4.99 packs are a great value to jump start your roster.
Don't buy the 5 - 330 packs, especially the faction ones. I've never had success with them.
When new characters (toons) come out they usually come with a pack you can buy in the store for real money, and a 5 - 330 pack for crystals. Those 5 - 330 packs are a gamble and I don't risk it.
Buy crystals when they are have promos running that give you an extra 25% return (sigh, where is my vault, sigh), or only buy vaults for the value. A vault can last you a very long time if you are conservative.
It may not make sense for you to spend crystals on refreshes at your level. At 85 it is a no brainer, and I use those refreshes to farm gear salvage for the most part.
Hope this helps. Everyone has a different approach. Hope you enjoy the game!