The F5 is my favorite Nikon SLR, so nice to use, capable, but still very simple. I found it really excellent with the 105/2 DC you've got- it's great with all the Af-D screwdriver lenses. The AF system is fairly simple, but it pays to read the manual or some other guide to understand how it works in the various modes, and play with the camera a bit to get a feel for how big the focus points are- I always found that they were slightly larger than indicated in the finder.
Getting used to the somewhat primitive display of the active point can be a trick too- as the LCD just makes the active point a little darker, rather than highlighting it in red. In practice, I would sometimes have issues if I bumped the selector in the back and moved away from the point I wanted, it was hard to tell in the moment which one was active. My solution was just to lock the camera to the center point nearly all the time, and use the focus mode that let the AF system automatically switch points to track- which worked amazing for the action I usually photographed. Just check it out, get a feel for how it works, and hopefully have some fun! I'm going to dig out one of mine and run some rolls through it, too.