So there are a couple of things to bear in mind.
pluripotent does not mean that all genes are active. It means that the stem cells have the ability to form different cell types. However, it still needs to keep the cellular programme of a neuron for example silent. So the epigenome is still present to keep other cell type programmes silent until there is a ...
No and Yes, respectively.
No, you don't need to select for and generally you can't unless you use something like FACS to sort and capture cells expressing your marker/GOI.
Transient transfections are generally not selected for, if they are it is to make a more stable line, and either requires integration of the marker site into the genome (most common) or in ...
Heterogeneity is a noun meaning:
the fact of consisting of parts or things that are very different from each other
In scientific use the context determines what is differing.
The context here is gene expression in individual embryonic stem cells (presumably single-cell RNASeq). Here the heterogeneity in expression would be for the genes
…(Neurod1, Klf4, ...