2. If an attack is neutral to the spider, then the spider divides itself, the other jutsu ends, and you get two spiders (spending chakra enough for an S rank)
3. If the attack is higher, it happens the same as 2. Or does it end the spider?
Yeah, however for three, it is pretty iffy, like idk but the time frame might be reallllllly tight. Cause if you spend chakra to get the spider back up and multiply it would cost a move, so by TF I don't think that is safe, unless you have a clone/ally/summon then it might work well. It depends mainly how you use it so you don't get yourself killed, but for the simplicity of the jutsu I doubt that will be the case.
4. Can I divide the spider at will, to have the incoming jutsu pass through it without touching it?
Nah, though for an update I might consider it.
Well, I'd just like it if the renewal cost was lowered. Maybe to half?
Most likely, and probably play around with the numbers. Anyway, thanks and have a good day.