Unzip it at any location that won't matter, you will have to access files from that folder within your project that is the only requirement. For development you would need VS Studio on Win and XCode on a Mac. Refer the documentation html present inside the sdk folder, it has all the detailed information on how to setup the environment, object model, also sdk ships with lots of sample plugin projects so the first step to test your setup would be build those and load the plugins on InDesign.
You may need to read my answer to an earlier similar question: https://community.adobe.com/t5/indesign/highlighted-text/td-p/11257455?page=1
Jongware, well sure code can be edited using any editor and for that matter even ESTK. But in that case we will have to set up the build system outside the XCode or VS like configuring the make build system etc (i have not done this myself). So i surmise your advice will send the OP down a rabbit hole at this stage, and might frighten him. If an IDE makes my life a bit easy then why not 🙂
By the way excellent points made in the other thread you linked.
I know there is a difference between the 2 (i've made several scripts for indesign) i just dont know what all i can do with the SDK yet. Having read the link i am obviously not ready to make a plug-in yet since I am not very well versed in C++. I'm still going to try my hand at it just because thats how i am but i'm not expecting to get what i'm wanting done quickly lol. Thanks for your advice and help.
THank you Very much