I'm sorry to tell you this but I doubt you will be successful. Purple fringed orchids are one of those that require a certain fungus to be already present in the soil in order to survive. Without it they die.
Don't mean to be a downer. But I'm pretty sure that's the reason purple fringed orchids aren't grown more in gardens for their beauty. Orchids need precise environments.

Ah, the seller said that they'll send some soil that the original plant was grown in along with the seeds.

In that case it'll probably have the fungus, give it a try!