Really depends on what you want your system to be, if you want a lightweight system choose a barebones distro like Arch, Gentoo, Void or any server spin such as Fedora Server. Then, during installation you only get what you need. If you are going lightweight you’d probably want something like Sway WM, Hyprland or XFCE.

If you don’t care for minimalism, then choosing a distro focused on a graphical interface such as Fedora Workstation will be much better for you, since that distro will be maintained with the idea of users using whatever DE it is, the distro maintainers probably contribute to upstream of the DE too. Support will also be easier since you’ll find that these distros, while maybe having smaller communities, those communities ask more questions and get more solutions due to the Linux inexperience.

It makes sense to install a Desktop Environment during the installation. If you install a really bare-boned Linux installation without DE you might even end up without a graphical display manager to login making things complicated for a new Linux user.

I heard that sometimes installing a DE after the distro installation can cause some issues because you may forget or not know some dependencies, additional packages and setup commands (like adding users for system apps). Because of that I would highly recommend installing a DE during the distro installation because in that case everything necessary is usually included and at least somewhat configured

What is your use case? For me, something like a fileserver which I am mainly SSH-ing into anyway, I may not install a DE at all, but if this is going to be a general-use desktop, I see no reason not to install the DE right from the beginning, and selecting a DE will be part of the install process of most Linux distros, or some distros have different install disk images that you can download with any given DE which it supports.

If you are very concerned about keeping your system lean and want full control of what gets installed, you might want to look up guides for installing Arch Linux. The initial setup process is more involved than other distros, but once you have it installed, I think its reputation for being difficult is overblown.

The beauty of Linux is that you have choices. You can easily start with something very light (I’d recommend XFCE), then install any number of other desktops.

As others have said tho, use a VM or WSL first. Test things out with different DEs, see which you like, then install those on a live system (just to avoid having numerous DE’s on your final install).

You can do either. Just look up your package managers name for the full environment to install so you don’t end up with just the window manager or something.

The general idea is that a desktop environment provides you with common graphical user interface elements such as icons, toolbars, wallpaper, and desktop widgets. In other terms it’s purely an aesthetic question. You can also decide which of these features will be useful to you and install the appropriate package(s) if you don’t want to grab the bundle that comes with any DE.

As far of timing is concerned, you can always experiment and install what you need as you go. The only downside to wait will depend on how good your distro is in managing packages dependencies.

Personaly, my Linux journey made me realize that the features offer by a DE were actually negatively impacting my productivity and a windows manager (a tiling one for me) was all I needed. But this decision - like a lot of others - comes down to personal tastes. Note that not using a DE doesn’t mean relying on the terminal only.