But how do I get all this from not installing to my root then? If I have everything installing into the root, then I won't even be able to install 1/4 of what I want...also when I have to upgrade it'll wipe everything I did install
You don't really but you don't need to. True you will have to download again. But one thing I love about linux is it is nearly exponentially easier on hard drive space. I have a virtual machine setup right now. In windows with what I need I'm sitting at 53gb disk usage, another 15gb in media on top of that. In my debian virtual machine root is only sitting at 5 1/2 gb. That is with the same "functionally" programs on each. Can do same task on whatever I feel at the moment. 53gb vs 5 1/2gb. Same selection of software. Not even close. 20gb should be more than enough. If you are worried about steam games I believe they do install to home.
Another example, again with debian. I have terrible internet. I can do a clean install + full updates + all software I need in 2 1/2 hours or so. Windows same thing takes me nearly a full day. Almost all download time. An idea of the difference in amount of stuff on each one. If I had to guess this is all due to shared libraries.
To be safe maybe re-install and make the root a bit bigger? But the average
user won't even come close to topping out a 20gb root I would guess.