I am still learning, but this is what I have so far...
Tool number 0 is predefined in PP to be no tool (spindle only).
Some people use high numbers (like 99) for things like Haimer sensors and edge finders. I prefer the low numbers.
I use tool 1 for my Haimer, and then my most used tools start after that. I used to have a couple edge finders (tools 2 and 3) but now I only use the Haimer. I have tools I use all the time (fly cutter, roughing mill. 3/8 finish mill, and they get the lower numbers, and then I have drills, taps and stranger stuff like the boring head after that. I don't leave open slots (so that I don't have to scroll as much).
When I assign a tool to a number, I leave it assigned to that number, even if I remove it from the TTS holder to use the holder on another tool (I have a few holders holders, but still not enough for every cutter). I retain the numbers in Fusion 360 also. That way they stay in sync. When I do use a tool's TTS holder for something else, I set the tool length in PP to 10 inches to remind me that it needs a holder and touched off again. Setting it to 10 inches is better than 0 inches, in case I accidentally select that number, it won't crash. As you may know, the PP tool length has no bearing on Fusion 360, although the tool geometry does.
In Fusion 360, I might have multiple versions of the same tool, depending on the material. For example, I have a tool folder for steel and a tool folder for aluminum, and the same 3/8 cutter and tool number in each, and each "copy" of the 3/8 cutter will have different speeds and feeds depending on the material. In fusion 360 I have pretty accurate geometry setups for the TTS holders and while the overall length (the PP tool length) isn't important, I do trey to keep the cutter length that extends from the holder accurate. Just to make sure that fusion 360 can detect a collision.
Bob