Hello,
Yes, absolutely. That's the point of "Niche Demos". Niche Demos are independent of each other but if you would still like to copy Elements from One Demo to another, you will need to Copy the CSS/JS as well. With HTML Templates, this is a necessary step, you will need to copy the relevant codes based on the Demo you would like to use or reuse elements. The Classic Demos have unified Elements with all the CSS in one place. But the Niche Demos are created independently and thus you will need to make additional adjustments.
With HTML Templates, the Codes you see on the Live Previews and the Codes you get in the package are almost identical (we just make some changes on the Live Previews like Switcher Integration and API Keys, rest all are same). The example you stated about Sandbox, they do not provide Niche Demos, all of their Demos are Homepages, and not Niche Demos. What we provide are Prebuilt Niche Websites which have distinct features and inner pages unlike same features and layouts on all Templates. Well, in any case, this could have been asked in the presale questions.
Well, one size doesn't fit all. Again, all the Design Options available are available on display before Purchase, so the Limited FAQs options have more flexible/customization capabilities than you think. Canvas can be as powerful and customizable as you want it to be. And most Templates replicate our coding structure any ways. But as with every HTML Templates, you will need to do the additional customizations.
Can you confirm i can use all the elements however i want without increasing css size unnecessarily? I don’t think so.
Well, you have answered your own question here. Doesn't that depend on how much you want to customize? If you go through the CSS/SCSS Files thoroughly, you will see we provide CSS Variables, which no other Templates provide, which are heavily customizable right within the Template. And you have the option to delete the CSS as you please right from within the style.scss File to make the CSS Slim or use PostCSS with Gulp. Every possibility has been provided, you will just have to use them. :)
Anyways, we better provide you with a Refund. Request it here: https://themeforest.net/refund_requests/new .
Have a Wonderful Day. :)