Can you tell us information about your app? we can't read minds, yet.

It is a platform in which user can exchange or sell their old items user post their items like a reels

Then that would require you to be on the Pro plan, since it is a business product.

Is their any way i can calculate the resources that how much my platform required

Run it on Railway and look at the estimated costs we generate for you.

For that i have to purchase plan first?

Yeah, you can go with Hobby for now, but you would eventually need to upgrade to Pro given your usecase.