Wheel/tire size upgrade advice

I'm bewildered by all of the threads about wheel and tire sizes, so I'd like to ask what others in my use case have done. I have a 97 Sambar KS4 with the stock wheels and tires. I purchased it in July to use as a daily driver for getting to my new teaching position that is 4.2 miles each way on a road that is mainly 45 mph with about a mile at 50 mph. I would like the ability to drive on dirt roads in the nearby Pisgah National Forest to go mountain biking. I don't want to lift the truck. First question: wheel size - 13" or 14", steelies or alloy? Second question: tire size? Specific recommendations appreciated! Note: I'm a lifelong bike mechanic who is learning to wrench on cars with this truck (and the help of this group, the mini truck forum and YouTube university). Thanks in advance for sharing your experience