You might wand to consider the resources needed to use a non-gnome file manager with Zorin 17 Core:
Of those named here, Thunar brings in the least load of extra packages - 18 new packages to support it. The worst is Dolphin, being a KDE application, requires 221 new packages to support it.
In Files, you can rearrange Bookmarks in the sidebar by dragging them to a new position. It's only the User Directories that are fixed alphabetically.