While Trish is completely right that the roughness can't be completely eliminated (you can't print a perfect spherical surface with discrete layers), the situation can be improved dramatically. The most telling photo in your question is the one of the removed support structure.
The part of your sphere that's seriously rough is all severe overhang. In this ...
Huh. On a hunch I just changed a copy of a .3mf model to have a .zip file extension, and what do you know, it works! 3mf is just a set of compressed xml.
The zip folder structure I saw included a MetaData folder. I bet you could put just about anything you wanted in there, as long as it doesn't conflict with things other 3mf parsers are expecting to find.
Open PrusaSlicer, go to Configuration -> Configuration wizard, then go to page named "Other Vendors", tick the checkbox next to the name "Creality", then click "Next" at the bottom right of the window. A page with a handful of Creality printers should appear including Ender 3. Tick the checkbox under Creality Ender 3. Then ...
You can't print them smooth
The short answer is: with FDM you can't make curves that go into the Z-direction. The better question is: Why?
Let's look at why it is rough: the roughness is from the layer height and the thickness of the perimeters (walls). At some point, perimeters of the given thickness have to be placed in a way that does not cover up fully ...
Basically all slicers work very similarly, it is a matter of preference, being accustomed, or wanting to use a certain (set of) features. Their job is to prepare the object to be sliced in layers to be executed by the printer you use. For every slicer to work properly, you need to configure the printer settings correctly.
Basically, all slicers have the ...
Do the two loose pieces go where the fill shows up on the larger piece? If so, you may have internal surfaces there that need deleting in your drawing so that they don't mess up your slice program. Otherwise, the slice program may leave a gap in the gcode where you have no extrusion.
If you retract too much, it can cause the filament to jam in the hotend, ...
The error message explains that you cannot print your objects sequentially as they are too tall for the gantry to go back to the bed level after the first object.
In other words, your clearance between bed and gantry is too small.
Minimum Travel after Retraction is exactly what it says on the tin: if the travel after a retraction would be less than 2 mm, it does not retract. You'll want that to be short, but not 0, because retraction can lead to under extrusion at the start of a new line, and every swap from one shell to the next shell right next to it is classed as travel.
As a software developer and 3D printing enthousiast I can tell you that indeed, like Trish said, the limit is your memory (RAM) and loading/slicing time depends on the cpu power.
RAM: keep an eye on the memory usage in the task manager/performance/memory tab. When it reaches the top of the graph, the application will suddenly crash and disappear.
CPU: The ...
This is most likely a hardware problem, namely the heat bed thermistor cable.
To confirm this as the root cause, here's what you can try
Reboot the printer
Move the y axis around to make sure there is freedom of movement at both ends
Jigger the thermistor cable around in multiple directions at multiple points on the cable
If you hit BED MINTEMP or ...
The bed minimum temperature is defined in your configuration file, e.g.:
#define BED_MINTEMP 5
If the error is displayed, it means that the measured temperature drops below this level.
What I am noticing is that upon finishing the first print
This could hint to a faulty heatbed connector where the connection is lost because the bed moves to the end ...