Yeah, ISO is not supported. Conversion of DSD content is discussed here:
Not sure about extracting DVD Audio, but there are certainly tools. It’s a pity you’d have to do the work though for the ISOs.
Chromecast is supported by Roon:
It’s Roon Tested though, not Roon Ready, so you can’t include it in an output zone together with fully Roon Tested Ready devices. In case this is a limitation for you. You can always use an old phone with Roon installed and 3.5 mm output. I do that in the bathroom with a repurposed TV soundbar. Works fine and is a fully Roon Ready solution (RAAT protocol zone) that can be grouped with the main system for simultaneous output. Else, some Raspberry Pi (if they have 3.5 mm out) with Roon Bridge installed maybe. There are RPi experts on the forum, I am not 
As for the memory consumption, there always seem to be cases on the forum where people are affected (sometimes with Linux as well, dunno if it’s the same on Mac), but clearly not everyone. I don’t have Windows (using Roon ROCK instead, and no such issues for me), so no idea what the causes are and if there are solutions, but take a look at existing threads: Search results for 'memory consumption windows' - Roon Labs Community
You could try installing the Roon Server package separately on Windows, and the full Roon app just for the GUI. Then the full app connects to the external server, on the same machine. It may or may not help, but worth a try. And it is the preferred solution anyway, as you can quit the GUI app (or it can crash if that happens) without the music stopping. Incidentally, this is going to be the future default configuration anyway, and there is currently ongoing testing to streamline this for easy installation with one installer.
Else, have fun!