Not too early to be thinking about butterflies in your garden. Providing larval and nectar foods for them is the way to attract them.
Try to choose seeds that are native to your area since those are the plants your area butterflies have evolved on.
Don't buy bedding plants that have been treated with pesticides/herbicides. Here is where you may have to do some homework. For example: Large box stores order bedding plants that have been treated with all kinds of chemicals to keep them "fresh and alive" looking for longer periods of time and have been treated with pesticides so insects don't spread in such cramped, tight and high volume areas.
These types of treatments may be good for the consumers eye, but lethal to the butterfly and bee.
The Garden Junkie has butterfly garden seeds in a fun little package .