Great picture. Balancing exposure - shutter speed, ISO and aperture is always a bit of a challenge for this type of photography. One method to try is using the 500 rule - divide 500 by focal length to get the shutter speed (for a crop sensor (D3400) and 14mm lens this would be 500 /(14*1.5) = 23 seconds, say 20 seconds. This would be the maximum shutter speed to avoid star trails. Adjust apertures and ISO to match. Give this a try, and good luck for this evening - I shall look out for tomorrows posting.
Thanks so much for your comment yesterday!