1) Theme is not working properly? Plugin not registered
Ans) Are you running your theme in registered Domain. Please recheck your Domain with Registered Domain.

2) The theme is working but only when I disable/uninstall the mega menu. (Internal Error occured)
Ans) You have to uncheck Topic page in admin panel Goto admin panel---Content management----topic page-----Find page----include in top menu (uncheck)----Save

3) How to disable/hide manufacturer on home page?
Ans) It can be hide one by one not full panel get disbled or hide Steps are given below: Login Admin Panel-->catalog-->manufacturers-->Select Particular Manufacturer-->Published (uncheck)--> Save

4) How to change store information?
Ans) Goto Admin Panel--> Configuration--> Stores-->Edit(Information) According to your store

5) How to change site title?
Ans) Goto Admin Panel--> Configuration-->General & Miscellaneous setting-on clicking-->SEO Setting-->Default Title --> Change accordingly

6) Error Email validation Link?
Ans) Goto Admin Panel--> Configuration--> customer setting--> Registration method-->select email validate from drop down

7) How to remove estimate shipping from checkout page?
Ans) Goto Admin Panel--> Configuration-->Setting-->Shipping Setting-->Estimate Shipping enabled (unchecked)-->Save

8) How to manage cutomers address field?
Ans) You can create and manage the address form fields available during checkout. Goto Admin Panel--> Configuration-->Setting-->Customer Settings-->Select address from fields Tab-->Select fields accordingly-->Save

9) How to remove instore pickup from checkout page?
Ans) Goto Admin Panel--> Configuration-->Setting-->Shipping Setting-->Pick Up in Store" enabled(uncheck)-->Save

10) Mega Menu plugin not Registered ? Please Register Your Plugin.
Image Zoom plugin not Registered ? Please Register Your Plugin.
Quick View plugin not Registered ? Please Register Your Plugin
What can i do to solve this problem?
Ans) If all Plugins are registered, Plugin not registered showing that was only due to cache issue or slow speed of internet.

11) Could someone give some info about the better approach to use with the theme?
For example I would like to know what's the size of pictures in thumbnail and details page and zoom pictures to improve the experience of the customer .
Ans) You can use images size nearby 415*415.

12) I am using nopCommerce 3.7 and copied correct plug ins from 3.70 folder only. I am able to see theme in admin but not the plugins.
Ans) Please check out below mentioned points that you have done proper or not. 1) Visual Studio (minimum 2013) 2) SQL server (For database) 3) Database connectivity 4) Folder of 3.7 version Theme (Step by Step) Process.

13) I accidentally deleted the admin user. How can I get back in as admin?
Ans) If you have access to the database (using a tool like SQL Sever Management Studio, etc) then un-delete the user: update Customer set Deleted = 0 where Id = 1 (Typically the Id for Admin is 1, but if not, then find Id, or use the Username - e.g where Username = 'email@domain.com')

14) What do you for selling by sizes, colors, material, etc., specification attributes or product attributes?
Ans) Product attributes will do it. Don't forget to set Manage inventory method: Track inventory by product attributes in product info tab and then to define stock in the product attributes>combinations tab.

15) How to add tier prices?
Ans) Tier pricing is a promotional tool that allows a store owner to price items differently for higher quantities. Goto Admin Panel-->add product-->Save & Continue-->Select particuler product & Edit-->From bottom of page-->Select Tier prices panel-->add new record-->insert all required information-->update-->Save

16) Apparently if site is configure for SSL and you append any ‘http’ source it break the shopping cart.
Ans) I appreciate you if you consider to change following in your plugin files.
File Name – DefaultPicture.html
Line number 6
Correction - Html.AddScriptParts("https://ajax.googleapis.com/ajax/libs/jquery/1.8/jquery.min.js"`);