Hi,
For a normal 300dpi photo with 4288 x 2848 is around 6Mb now with 30" x 20" the number would be 6Mb x 4 X 8 = 192Mb or with color depth say around 300Mb. 16Gb of RAM minus manything gives you at least 8Gb, should be plenty. Just for testing, please reduce your scan down to 300dpi to see how big the file is. The scan process could take a lot more, which is similar to sending a 1Mb Word file to a printer, this would end up 30Mb down to the line.
Regards.