16GB RAM for sure - that's a no brainer.
Not sure how some people could possibly suggest base 8GB. You're keeping it for 5 years.
8Gb will be fine in 5 years for workloads it's fine today. RAM requirements are increasing much slower now then a decade ago.
16Gb is a good idea, but if they are fine with 8 now, they'll be fine for years to come.