How can I setup this flow for shipping choices?
Free shipping orders over $50
Have a look at the flowchart attached.
For your weight-based shipping
You can set minimum and maximum cart total weights for your flat shipping rates. You can only set flat rates depending upon your cart weight.
For your free shipping on orders above $50
You need to go to Settings > Shipping and delivery.
Then go to the shipping profile where you want to add a free shipping rate, click Manage rates.
Add the shipping rate to each shipping zone where you want the free shipping rate:
Then Click Add rate. After that Enter, the name for the rate, make sure that the value of the Price field is 0. Then Click Add conditions. And the Select Based on order price. Enter the amount $50 as your minimum price. Then save it.