If you intend to really use your machine with ease I think these are essential:
Dust collector, not just for cleanliness and machine life bit for quality of cut as well esp items/projects using small bit like 3mm or 4mm
Controller is the brain of the machine, better off buying OF as it is already plug and play, you can buy other controllers but you need to fix some settings before you can use the machine
Joystick for me is essential. Operating the machine is way easier if you have a joystick esp if you run short programs and make frequent set up of materials
Wifi and laptop is essential, file transfer, file editing, control, everything is again way easier although you can use the OF without laptop or wifi, operation is more seamless if you have wifi and laptop. You can just use the small touch screen on the OF as is anyway you would most time will prefer to interact with The OF via laptop.
Journeyman size is my dreamsize for OF just because I do projects that is about 1.2M long, I have ax X35 Woodworker, it takes a lot more skill to to set up and program if your material is longer than your machine but it can be done. Its just tiring if you do a lot of the long ones on a small machine.
Spindle watercooled for me is essential if you run regularly like almost 8 hours a day everyday and if you want less noise, automatic Gcode control of spin ( you need to learn first the right speed and feed for the bit, based on wood type, and your design quality finish needs). Spindle is life but then again Im not a hobbyist, I run a small production operation and I have time and some basic knowledge to set up the VFD so Spindle can run on GCode plus the collet is E typ, hold is tight and centering is accurate plus no carbon brush.
Lighting under the router/spindle is essential, those shadows and poor lighting will slow you down when setting up the work piece esp if you use the same Workpiece location.
Cable management is essential, although you can run your machine as is, dangling wires is dangerous and may cause you damages even to your product is the machine stops or malfunction during a cut.
I use Carbide Create, works for me but it all depends on what you will cut. I mainly cut just 2D.
Air filtration system is essential for health and cleanliness