Welcome to the sport. Now turn around and leave before you end up with more gear then the local academy, and a lifelong obsession for "just a few more birds"
That being said - there is some good advice here. Use your academy gift card to buy as many game winner Texas rig decoy weights as possible. You won't find a better value, and making them yourself won't be cheaper or better quality. If you are planning to walk in, look at getting a nice decoy bag. Avery sells one in the $50 range that will hold 30-40 decoys and is PADDED. Do not buy the game winner brand, trust me on the Avery bag. It's huge, padded and comfortable - and worth the $20 the first time you walk a .5 mile each way.
Now to get to your question, and please no I am speaking about coastal decoys... Or decoys that can be used in Texas and still be fine.. Mallard decoys will be less then useful on the coast, and honestly, you can get away with wigeon/gadwall and pintail decoys when hunting for mallards, so, invest in those for being used everywhere.
As you are just starting out, I would really target what you can get quality and quantity wise. You can always upgrade later. I mainly have greenhead gear decoys, but also have flambeau storm front and tangle free brands scattered in my collection.
Judging by your situation, I would like and see if I could fin the different puddle packs from greenhead gear to give you some variety from start. They have different versions with teal, wigeon, gadwall, pintails and mallards sprinkled in. I don't think you need the version with mallards, but, was more telling you that a version existed.
I personally would stick to those brands in whatever you can find on sale. I would buy wigeon/pintail decoys first, followed by blue bill, gadwall and redhead decoys. I may get laughed at for redhead decoys but I think it adds realism when targeting pintails.
Greenhead gear is my reffered brand over all, though I will say the flambeau storm fronts are nice and are holding up fair. Tangle free pintails are nicest decoys I own (most realistic in my opinion) and are even better then the pro grade green head gear decoys.
Again, as its your first start, there is no need for pro grade anything, just check macks and Rogers sporting goods for end of season sales. I have also picked up some decent green head gear puddle packs from cabelas bargain caves a time or two.
Right now it's about the sales. I remember when I was first starting out and academy carried greenhead gear, two weeks before season was over I would have my local academy order all the pintails, redheads and what ever green head gear decoys they had from the other stores. By the time they arrived, they would be 30% off.