If I cast Mana geyser, then cast Insidious Will targeting the Mana Geyser, then cast both sides of Expansion // Explosion with the expansion side targeting the Insidious Will again, which is targeting the expansion/explosion, does this go into an infinite loop? Lets say for the examples sake I am making the X=10 and have 3 opponents in this commander game. Does this mean I can pretty much do infinite damage and card draw to the other players??
You can't cast both sides of Expansion/Explosion. It does not have Fuse so you just choose which side to cast. If you cast the Expansion side targeting Insidious Will, you get another Insidious Will. The only things you can target (that will still let the copy resolve) are the existing Insidious Will and the Mana Geyser. You can't target the Expansion and have it resolve since it is already resolving and will leave the stack before the new Will can resolve.
Since there seem to be some important issues with the premise, I am not sure it is worth going over the rest of the situation.