1) Right, do not use handob reference <= 120, as there are 16 vanilla handobs defined, also the first 16x8 = 128 sprites are reserved for vanilla (from 0 to 127)
So, except if you are intended to replace a vanilla handob (even in this case I would not proceed like this, but I will not explain because I am quite sure it is not your intention), use a handob > 150
As sprites number do not suffer of interference between two different mods (i.e. two ruleset), you can always make your handobs start from 150 (or 200 if you prefer)
Then you have to apply an increment of 8 between two handobs declared inside a same ruleset
And beware not to go over 10002) Then, be careful about case sensitive, especially regarding path and files
I can see
Bla
bla.
gif,
Bli
Bli.
GIF, ...
If you want your mod to be usable by Linux users for example (there are many on this forum), it is recommended to be rigorous with filenames, and to pay attention when referencing them in your ruleset