https://helpx.adobe.com/experience-manager/using/programmatically-accessing-cq-content-using.html

You can write osgi service to read data or java  classFor osgi service alot of articles are available there, do checkhttp://blogs.adobe.com/kmossman/2012/04/osgi-sling-service-example.html

As I mentioned earlier sighlty was introduced 6.0 onwardsSightly API which u are using (WCMUse) will not be available in 5.6.1 and thus you cannot useYou have to use AEM 6+

It works on listener, as high level you need to apply listener on which you want something to work.Now in this case you will a add listener on check box so that a particular action can be performed.For Classic UI you need to use widget listeners, check widget documentation https://docs.adobe.com/doc...

These are sightly APIs which were introduced from 6.x onwards.Although there is feature pack of sightly available in 5.6.1 but that is just to see sightly preview and wont support sightly apis completelyTo get code working you need to use AEM 6+, Check release notes here https://docs.adobe.com/docs/...

How are you getting JSON and where?As per parsing you cannot do in component html file but can be done easily in javascript use api file.But share more details.

Sightly provides similar for loop which can be used.1. You can either use data-sly-list provided by sightly, Documentation2.Or put you business logic for JSON in javascript use api file. You will have access to all data and api you need to generate json ( Should be easy to use and maintain but hard ...

1.Yes, to ensure try with the OOTB text component** Make sure the component which u r trying to include in component html should have dialog 

This might help you:Classic UIhttp://experience-aem.blogspot.in/2016/01/aem-61-classic-ui-limit-components-added-in-parsys.htmlTouch UIhttp://experience-aem.blogspot.in/2016/01/aem-61-touch-ui-limit-the-number-of-components-added-in-parsys.html

It should not be a problem, you can have different dialogs for nested component ( when one components is included inside another )