Hi @Varada Thakur,
The Microsoft 365 developer subscription has the same licensing and capabilities that a regular Microsoft 365 E5 subscription.
The storage limit as per this article:
User and application throttling are explained in this article:
There is no difference between developer subscription sites and actual SharePoint online sites Rest API response time. And I searched around but I didn't find any articles which explains specific data on Rest API 1.0 response time for authentication and other POST/GET request.
Hope my answer helps.
Have a good day:)
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