You are a PC guy? Well, political correctness isn't that bad, or is it?
Maybe this is why they were dirt cheap. Because they are outdated and too slow.
RAM upgrade, easy and cheap.
Instead of a hard disk upgrade, you could buy and external disk, or a hard drive plus an external enclosure, which you should have anyway for back-ups.
Processor upgrade? Have you checked out what is available for this model?
Instead of pouring lots of money into a rather old Model, have you considered getting a used, or even better, original Apple refurbished iMac?
So you might be better off selling the eMacs dirt cheap, and get a more modern mac. If you want to get a feel of a mac, the eMac won't do.
Because once a computer has reached a certain age, all the upgrade possibilities you have are equally antiquated (except the professional towers, possibly)
Above all: how much computer do you need.
Tell us: what kind of applications do you plan to run? If it has to do with photo or video, your eMac may, even after upgrades, be too slow.
First step: consider your budget.
Second: how much would you have to spend on a refurbished iMac (go to apple.com, click "store", and on the left side of the page you'll find the link to the refurbs).
Third: check the upgrade costs.
This way you'd get at least a quick computer with Superdrive. And a much better screen.