It sounds like a fun event!
The first thing to consider is that there is not one kinda universal setting; f/stop, shutter speed or focal length, that will cover any particular lighting situation, especially in flash usage. Even the way you employ your speedlight; directly, modified with your home-made rig, or bounced for ceiling or wall surfaces is dependent on the conditions in the room, the height of the ceiling, the size of the room, and the proximity of the walls to the subjects.
So...I looked up the manual for your speedlight and found that it is TTL capable and, assuming you have the model that is comparable with you Nikon, camera, it should automatically address the exposure issues for flash usage. That means it should provide correct exposure, taking into consideration the required f/stop (aperture) for sufficient depth of field as per your determination and setting, and the distance between the camera-mounted flash unit and the subjects. This should also work with a modified flash or various bounce situations.
Practice: If you can visit the venue in advance and test things out with just one person as a test subject, you can determine if your basic mode settings are correct. Function rooms and halls in various venues can be diverse as to room dimensions and ceiling heights as well as existing light availability. Testing in a shopping center or other space may not coincide with what you will find at the actual location.
While you are at home, you should read into the manual and make sure you understand the basic setting-up of the various flash modes in the speedlight. You can test to see if it is basically operating properly. In case you don't have the manual, I will attach a link where you can download it.
If you can access the location ahead of time, even while the catering staff is setting up, you should have enough time to make a series of tests at various distances, different focal length (zoom) settings and trying direct flash, modified flash and bounce flash and see which is most suitable as per your own taste.
You may need to increase the ISO if your test results are consistently underexposed. Make certain the shutter speed is within range for flash synchronization.
On events like you are describing, here are some suggestions for a good coverage: All over shots of the room, guest mingling, a few posed groups, folks can pose at the tables (not while eating), some detail shots of things like buffet tables, Christmas trees and decorations, anything related to amateur radio gear or paraphernalia, any speeches, presentations, gift exchanges, and any dance floor activities. Think about telling a story or presenting a slideshow at a future meeting etc.
The speedlight you have seems to be a good quality model with enough power to handle some bounce light techniques.
Do a few preliminary tests and let me know how far you got and I will try to address any further questions.
Link to manual.https://www.manualslib.com/manual/1103446/Phottix-Mitros-Ttl.html?page=2#manual