I would say that is right, the phone starts at 1000 for the 128 gb version and 1250 for the 512 version. The normal down payment is 250 so that makes sense to me.
The down payment may differ. The best advice I can give would be to log in to your My T-Mobile account and act as if you're going to purchase the device. From there, you should be able to see the down payment required. Even if you're trading in a phone, the down payment amount will stay the same.