Within the SharePoint Designer you have Export Workflow option available that can be used for this purpose

The account of user who created and published that Workflow

This is not true. You can create and publish SharePoint 2013 workflows using System Account, however System Account can’t execute Workflows, once published

You can create SharePoint 2010 Workflow, which is using that action and then within SharePoint 2013 use “Start a List Workflow” Action to execute 2010 workflow

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2) i) MOSS stands for Microsoft Office SharePoint Server.
 ii) It is the complete version of a portal-based platform for collaboratively creating, managing and sharing documents and Web services.

3) Yes. The Managed Metadata Service application enables content types to be simultaneously published and consumed between different farms.

1) Open SharePoint 2013 Management Shell with Run as administrator. Copy the following command and paste it.
Add-SPSolution “Your WSP Location”\”Your WSP Name”.wsp.
e.g
Add-SPSolution -LiteralPath “C:\Users\TestWSPFolder\MyTestWSP.wsp”

2) Go to Solution Management in SharePoint Central Administration. Your solution is added to Solution Management.