Yes, it most certainly is supported in development stores.
No, there is not a specific store type.
No, it is testable prior to submission and is a requirement that it works properly before you are able to submit.
If you have managed pricing implemented properly, you’ll be able to call the managed pricing endpoint which will ask the user which plan they wish to subscribe to. At that point, they will be asked to confirm the selection and when confirmed they will be charged (it’s not a real charge in development stores and it indicates this as well). You will receive an email once the process completes.
Be sure you have your pricing tiers setup properly in your app submission (as you are preparing it and before you actually submit it). Also, be sure your features follow your pricing tiers as I’ve read this is one of the reasons to be denied. Finally, make sure you have a pricing page on your web site such that your potential users can reference that as well.
However, there is an issue right now that our developers are aware of with Plus Development Stores created on Partner Accounts in the Dev Dashboard, where they are receiving the "This feature isn’t currently available for your store” error message unexpectedly.
As mentioned this is something our developers are aware of and are working on a fix further at this time, and we are currently monitoring and discussing this issue in the following thread:
I will be closing this thread as it is a duplicate of this existing issue, and any further questions can be asked in the thread linked above, and any updates to this issue will be posted there as soon as they are available.
That said, in the meantime, this error is specifically only occurring with Plus Development Stores created by a Partner Account in the Dev Dashboard, so you can work around this issue with the following:
Create the Development Store via your Partner account and select any Shopify plan other than Plus for the development store features, and test charges should work
OR, create the Development Store via a Merchant account, and select Plus or any other Shopify plan, and test charges should work