Wondering about the most straightforward way to take a list of genes and create a GRanges object, so basically pull the intervals for lets say a list of 500 RefSeq genes? Thanks!

It depends on the source. For RefSeq in particular, you could use GenomicFeatures::makeTxDbFromUCSC() and ask for the "refGene" table (I think that's what it's called). Then, extract the desired features as a GRanges with e.g. genes(). There are probably resources available from AnnotationHub, as well.