One: Trucks stops can, depending on factors I do not fully understand, be much, much further than 8 hexes apart. A single L2 truck stop pushing 50% LP/LIS/truck points along a sealed road can push enough supply to keep a brigade and a half fighting fit over about 15 maybe 20 hexes (have deleted that save so cannot check). I know this because I had a Siwa class where I started at the top of the map and, after conquering a couple of nearby majors, had to conquer down the map about 20 hexes to reach the other minors. Map did not allow easy east-west movement from my starting position.
Two: rail lines are shown on the map physically. However, there is no way to view the effects of just your rail logistics. I find this pretty annoying personally and it makes it hard to evaluate whether railways do anything my roads were not already doing. Not sure exactly how far rail can be spaced either.
That said, more truck stops is probably good. Note you can only build 6 hexes away from a city without penalties. After that point, you take penalties to your ability to govern a settlement (basically a modifier gets applied to your governor's skills and rolls). This is called administrative stress. It goes from 0-100% but takes effect in decile increments (10, 20 etc. 29 is no worse than 21). Ideally you would want your cities all spaced exactly 7 hexes from one another with a truck stop in each one.