Import previous work (WP Website) into one single Multisite

I have Multisite (website A) + New Blog Template plugin installed. I am a web developer with alot of WP based website. If i create a new site under website A, then I will get a blog with default template as I have set in the new blog template. But I wonder is it possible if i want to migrate/copy all my previous website (which have different theme/plugin) into website A (multisite). It would be easier for me to manage every single website under one multisite, but the for my previous website, the theme/plugin of each of my previous website is totally varies from one another. I hope u understand my questions.

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