The advantage of trimming, as just suggested, is that you allow to open faster.
Other than a small delay when it opens (to initialize the Icons Pane), TreePad suffers no drawback from the use of a large icon library, I can attest.
Now, I have not tried using TreePad with a large icon library on a very slow computer. So, if your computer is a bit on the slow side, then it should pay off to be prudent, and increase the size of the icon library little by little.
Suggestion: As you now have a safe copy of your default TreePad icon library, <treepadlib.tpz> (the file in H-1, above, is your safe copy), you can use the file <TreePadDir\treepadlib.tpz> for a bit of testing (i.e., the file used for testing will be the one standing in the main directory of your TreePad program). When the testing is over, then please remember to rewrite the file <TreePadDir\treepadlib.tpz> with your H-1 file, <TreePadDir\default_tpz\treepadlib.tpz>. (In other words, copy your H-1 file, <TreePadDir\default_tpz\treepadlib.tpz>, over the file <TreePadDir\treepadlib.tpz>, once you are through with all the testing you wish to do regarding the number of icons that you can have in the Icons Pane.)
Suggested Test: Following the procedures in All Users, add from 50 to 100 icons, each time you open TreePad. Then, the next time you open the program, first observe how fast or how slow TreePad is opening. If it has not slowed down noticeably on opening, then you repeat the first step (i.e., adding icons as explained in All Users). Then, the next time you open TreePad, again remember to observe the speed and, if all continues pretty normal, repeat the first step once more, and so forth, till you have placed in the Icons Pane the number of icons that you'd like to run the program with, as a rule. (If you intend to use the file in H-2, <TreePadDir\MieNet_motor_racing_tpz\treepadlib.tpz>, your test needs to reach 1500 icons, approximately.) Going one step at a time, as suggested, you can feel how your system performs at each change.
Note: If your system is not slow, there is no need for the above suggested test.