With the G. E. C. K. you can do all of the those things. There is a resizing setting for all objects, players, etc. Thus you have a super-mutant and a Super-mutant Overlord and the jumbo super-mutant two stories tall, a radscorpion half the size of a Giant Radscorpion. When you decide to add a few extra raiders, Super-Mutants, etc. you can choose what proportions you want them to be. If you want to see the how big you can make them it would be possible to make a Giant the size of the Giant in Jack and the Bean Stalk. Just resize a super-mutant to the largest number possible, rename him Jacks Giant, and go see him standing out the middle of the plains half way to Paradise Falls from the gate at Megaton.
Or make one Giant ant normal size, so you cannot see them crawling all over the Giants feet even if you got so close you could see under the giants toenail.