You willl need the forms add on to use adaptive forms from a license perspective 

You need to enable core components search for “ enabling core components on AEM forms”

The best option is to open it using Adobe PDF viewer. Previously browsers would allow Adobe PDF viewer to be the default PDF viewer, hence you may not have had this problem

I just tried the form you provided in the link using Acrobat and it works fineis it happening when you open the form using the pdf viewer of the browser?

I was able to delete the roes using the UI when you add a table to the form you get header row and 2 rows which can be deleted using the UI

we currently do not have any out of the box way to extract the data from SharePoint and use it in Adaptive Form

https://experienceleague.adobe.com/docs/experience-manager-cloud-service/content/forms/integrate/services/integrate-aem-forms-with-adobe-analytics.html?lang=en#capture-custom-events

I think it’s mainly for the analytics integration I can send you some additional documentation on that

Not possible you can restrict access to the rule editor for all the forms not on a per form basis

you can prevent some authors from accessing the rule editor. you cannot prevent people from accessing the rule editor and not making changes https://experienceleague.adobe.com/docs/experience-manager-learn/forms/adaptive-forms/restricting-rule-editor-aem-forms-technical-video-use.html?lang=en