I'm tempted to purchase a Powerspec Ultra (Flashforge Dreamer Internals) from Microcenter, but the one thing that's stopping me are the compatibility issues with S3D that I read in other posts. As of today are the machines and softwares fully compatible, or do I still have to downgrade to the firmware? Can I print over usb and/or wifi?
As far as I know, they support the 2.3 firmware, but not 2.4. I don't know anything that changed in their 2.4 firmware besides silly USB stuff that broke their communication with all previous versions of FlashPrint (i.e. you can't use earlier versions of FlashPrint with a v2.4 printer either). So personally, I would but the universal v2.3 firmware on my printer in a heartbeat, since that makes it compatible with everything.
But if you really want to use v2.4, you can still use S3D for all your model processing and gcode generation. Then you can just send the actual file to the printer using FlashPrint. That way you can use wifi too, but you still get all the benefits of S3D's superior slicing and control.
I have this exact printer and haven't had any issues. I always print via SD card so i can't comment on printing over USB. I can confirm it does not work over Wifi. Prints with ABS are flawless, working on dialing settings for PETG I still think it's doable