1. It still brings me to an admin login area instead of user login area.. If it is a plugin related issue what should I do? Does anyone know how to fix this please?
As said you should contact plugin developer to resolve this issue as we provide theme support here or you can consider hiring a developer to develop it for you. You can hire a developer from any freelance site. Colorlib recommends the developer https://www.upwork.com/freelancers/~011652ffec8865c6d5
2. “<!–nextpage–>” this code works only to split the post into more pages and what I need is I want to keep like 5-7 posts in one page. So I just need the option at the end of the page which lets me to go to other pages to read other articles.
Could you please share me the page URL from your site where it is displaying so that i can better understand it?
3. I thought that this forum is the right place to ask regarding Sparkling theme. If not how should I contact a plugin author please?
Yes this forum is the right place to ask regarding Sparkling theme but the plugin issue is not Sparkling theme issue so contact the plugin author regarding this.
If you don’t know how to contact plugin author then please share me the exact plugin name so that i can help you to contact him.
4. I have tried to use the code you provided “<!–more–>” it cuts the post but the rest of the text just disappears. What I need is a button which says “READ MORE” so when you click it you can read the rest of the post which was cut.
To display read more button for that post you can try using the CSS solutions shared in the following topics.
https://colorlibsupport.com/t/difficulty-with-read-more-summary-at-the-end-of-a-new-post/
https://colorlibsupport.com/t/read-more-tag-doesent-work/