Hrm, that's already two other Erzas....now I'm rethinking my plan to do Erza for A-Kon. Maybe I should put it off until A-Fest and use the extra time for a different Requip.
As far as sewing your first costume, the biggest three tips I can give you:
1) Take your time. Don't rush things.
2) Measure and fit twice, cut once.
3) The best cosplay is both functional and beautiful. Being comfortable, being able to move, and having storage (pockets, handbag, pouches) are invaluable to a good cosplay. Take those into account when making your cosplay.