I have already got Logos 7 Platinum base package and LN, do I still need Logos 7 Basic which is offered for free?
You already have the latest version of Logos. Logos 7 Basic is mostly intended to (get people to try out Logos or) get customers to upgrade from an earlier version of Logos.
But, Logos 7 Basic happens to also give you access to one resource that isn't in Logos 7 Platinum (likely because the paid base packages have better lexicons).
So while you don't need it, it's really a question whether or not you want access to that particular resource.
You don't need it but you may get access to one additional resource - https://www.logos.com/product/41596/a-pocket-lexicon-to-the-greek-new-testament - which isn't included in other base packages (though it is in various bundles)
Also, will this Logos 7 Basic be added into my current existing Base Package or it function as a separate software?
If you use the same username and password, it will be added to your account. There is no separate software... it is the same software.
You may also want to check out a recent article on the Logos Blog, "Should I Get Logos 7 Basic If I Already Own Logos?".
