Instead of you, I added the new custom step before and not after the Shipping Information step but I discovered the same behavior. Did you managed to solve it?
It should be possible to use the navigateTo(code, scrollToElement) function of the Magento_Checkout/js/model/step-navigator for this purpose.
Actual the next() function of the step-navigator.js is called in the setShippingInformation() function of the Magento_Checkout/js/view/shipping.js(which will be called by clicking the Next button).
In order to override this function you can copy the whole shipping.js file to your custom module and add the following to your custom checkout_index_index.xml.
If this does work, I suggest you to not override the whole shipping.js file, but extending it, like itself extends the Magento_Ui/js/form/form (Component). Then you should be able to just override the setShippingInformation() function.
I don't know if this qualifies as an answer but you can do what you are trying to do fairly easily in magento admin panel.
Go in Store->Configuration->Sales->Checkout->Allow Guest Checkout and set it to no after unchecking the checkbox that disables it.
Best Answer
Remove sidebar for only one step is not posibble you have to use custom js int your theme.
In your case, you have to hide summary block for first step using below code in your custom step js file.
add parent class so we can hide sidebar block
add css
.customer-step .opc-sidebar { display:none; }
Now you have to override step-navigator.js file into your theme.
in step-navigator.js file,
next: function() add line $('#checkout').removeClass('customer-step'); inside this condition,