No, you must logout to change desktop environments.
No to both.
Gnome-Extensions patch what Gnome removed, removes or is missing. There are no extensions in XFCE because XFCE is a full desktop - extensions are unneeded.
But you can install
sudo apt install xfce4-goodies
if you want.
If you give it a month or so, Zorin OS 16 Lite may be available.
Thank you, I have decided to wait for Zorin Lite to arrive, but gnome is very slow and it feels like there is no difference between gnome and Windows performance.
For me speed comes first and then looks. Privacy and open-source stuffs don't matter to me.
@Aravisian I just posted in the Ubuntu and GNOME rant what you posted here but better than me. lol
Even though I am still pretty new to Linux (Apr 2021), I could see what Ubuntu and GNOME were doing in my short learning time. As I said in that post, I have been around corporations enough to see signs of what direction they are taking. Once the word "lockdown" is added to a company's vocabulary, I know the path they are making and alarms should be going off in every FOSS believing developer, programmer and users head right then!
BTW, I use XFCE. 
I am very excited for Z 16 Pro LITE coming! I don't like KDE (buggiest mess and terrible "customizing" DE I have ever tried) and you already know my feeling about GNOME. But as stated by others here, Zorin took GNOME and really made it shine. I just like XFCE a bit more. 
GNOME.
Vanilla GNOME is dweebsville, but Zorin 16 and Pop!_OS dress it up rather well. And stock Ubuntu too.
I'm liking the look of Deepin Desktop Environment. How hard would it be to bolt that onto Zorin and give it a try?
I like them all for existing - variety is the spice of life. Personally at this moment cinnamon is alright for me, a KDE Plazma is probably the best, xfce is ok and gnome is not to my liking. Not tried MATE yet or the many others.
I would have to go XFCE. It is just a good work horse de. Easily set it up to meet your needs. My only misgiving is that lately I can't seem to get the XFCE sensors to work on start up.
I also like Enlightenment for it's small overhead. I've run into small issues every time I've used it though (like the XFCE sensors not working at start up).
Plasma is nice - is stripped down like in Kubuntu 18.04.3 - fairly small overhead.
Now I go off the deep end with Fluxbox and ICEwm.
Mate is okay if done well. Lxde was okay. I don't get lxqt as it seems to take more overhead than lxde.
Unpopular on this - probably: don't like gnome.
For me GNOME is the best and XFCE is good too.
Im watching a lot of YT reviews and i really dont understand all the hate gnome gets in youtube videos , it seems average users prefer it most of the time so it must have doing something right
It really isn't the DE as much as it is the devs of GNOME that are hurting themselves. They are becoming more and more of the likes of M$ and Crapple. And they don't like anyone modifying their precious GNOME and make it a headache for those that make some QoL tweaks for it. The GNOME devs don't listen to feedback and think everyone else is under them. As a DE, GNOME can be good and much improved and a great DE but unless the devs get their collective heads out of their butts, distros (like Pop OS) will move away from GNOME.
I used to be a fan of Gnome, but for heavy DE I would opt for KDE and LXQt over xfce. I was a fan of Gnome because of its superior accessibility app Orca, the screen reader. But now Devuan offers screen reader for the installation too and Orca works in KDE, LXQt, xfce and Gnome flashback. Why LXQt? Because it uses KDE libraries. 
I like Cinnamon and MATE. XFCE is okay too. I currently have Gnome with Zorin 16. I know Gnome is really solid as a DE. But, I get frustrated by the amount of resources that it uses. I think it's because it was really slow on Ubuntu, what I have used previously. But, it's okay on Zorin. It was really bloated before.
Zorin did a great job with Gnome integration.
I also use Cinnamon on Zorin OS 16
sudo apt install cinnamon cinnamon-core
I don't like Cinnamon or Gnome because of it's integrated Pulse Audio. Try to remove Pulse audio and the whole DE goes with it. However there is a workaround for Gnome not sure about Cinnamon. So for integrated audio read disintegration of the DE.
KDE Plasma Desktop is using 580 MB when idling with no applications running beside the terminal application. Whereas XFCE is using around 476 MB when idling with no applications running beside the terminal application
KDE Plasma Desktop offers a beautiful yet highly customizable desktop, whereas XFCE provides a clean, minimalistic, and lightweight desktop.
I like KDE as for the image side and it's not as bloated as others say.
Show your sexy desktop please 
, i love those eye candy colors in it.
Plasma
https://forum.zorin.com/uploads/default/original/2X/c/cb3f32931a57a09587178268633fceb9297f6194.jpeg
LXQt
https://forum.zorin.com/uploads/default/original/2X/8/829107bc8e5c6bc8dcf1ec06e62bef7672584320.jpeg
The plasma desktop looks so great 
I started out on Zorin so Gnome is what I first experienced linux to be, be that good or bad. I went through a phase of KDE as I got more into customization and that was fun going through videos creating different setups. I would distro hop to find which distro I liked using KDE the most on so setting my desktop back up each time was a bit of a time drag though. One day I deleted the wrong file and my laptop wouldn't boot up, O_O, and I was dreading another fresh install and setup so I came back to Zorin and Gnome to get something clean out of the box.
Come to find out, the forum showed me how to install new icon packs, themes, and cursors, which is about all I customized in KDE anyway, so I've been having fun with that and think I settled on something I like finally. Luckily Zorin offers some customization of it's own as far as orienting things so the combo really works for me and is all I need to get by happily. :]
cinnamon is hideous as sin and should be purge with an ugly stick. It screams windows 95 all over it. 
