Sachio,
First of all, let me congratulate you. It's really great that you're learning to save money! That's at least a 90 degree turn from what you had before. Now you only have to turn a few degrees further!
Second, I'm not a very good mustachian (yet), but I might help all our friends here with putting things in perspective.
The debt you have with 21% interest rate you really must kill. Asap. Really, no choice there. You know that already, so let's move on. You'll still have $1200 on your 'Stash! Plus, you'll be paying around $350 instead of $400 every month on interest alone.
Well, I'd love to know how much of your earnings you're able to save. Still, what I would recommend:
First, try to get a discount and pay your canal cash: you might still end up with $200 to $400 on your account for small emergencies.
Then, set yourself a goal: how much you're going to save every month?
Use half of it to pay your debts (credit-card at 6+% first, so you can get your interest spending down), and half you save to invest. As ScubAZ said, at first rebuild your emergency stash, then invest the money. Easy, no?
Oh, and do a test: for 6 months, don't make any leased purchase (not even zero interest ones). None. That's my challenge to you.
After 6 months, I'll let you buy things on lease at zero%, but only if:
1. You tried negotiating and the seller won't cut the cost more if you pay upfront
2. You have in cash all the money to buy it
3. Then you take that cash and invest for the duration of the lease
But that's after 6 months. Until then, we won't believe you're cured of your impulse-debts! :)