First, while you can edit any text file (.ini, .xml, .txt) with the dash, you don't need to do it that way when editing config.xml. You can do *most* right from the settings screen. The only thing you can't do with the settings screens are assigning the master password and configuring the menu layout -in which case, I highly recommend that you edit using your PC, then use IE to verify the structure. XML is pretty flexible but you have to follow certain rules.
DVD2Xbox/Complex Tools still has their advantages over UnleashX's basic disc copy. For one, they can read ISO9660 (AFAIK). It doesn't hurt to keep them at all.
Like any other app, you can keep EvolutionX as an app and use it when you need it, like running trainers, or flashing the BIOS. Also, like I mentioned in the document, you can try UnleashX first as an app and get familiar with it. Once you're comfortable, then, you can make it your default dash. Although it still has a few glitches, UnleashX won't and can't ruin your Xbox.