How Do I ... Get videos and articles from VTx in the same list?

You need to set the List component to "Build list using" Advanced Search and then paste the code below into the textarea after you edit the tag ID...this ID should be all lowercase and dashes and get pasted AFTER the colon in the property.value line above the group statements. The example has agriculture and life sciences.

path=/content/vtx_vt_edu/en
type=cq:Page
property=jcr:content/cq:tags
property.value=vtx_vt_edu:agriculture-and-life-sciences
group.p.or=true
group.1_group.property=jcr:content/cq:template
group.1_group.property.value=/apps/vt-common-page/templates/article-page
group.2_group.property=jcr:content/cq:template
group.2_group.property.value=/apps/vt-common-page/templates/video-page
orderby=@jcr:content/onTime
orderby.sort=desc
p.limit=-1

Changing the p.limit will change the number of returned results (-1 is all). The rest is fairly straight forward to figure out, with the property values having some paths and names you may not have seen before that are taken from the back end of the system via the CRX/DE interface.