Ok I really shouldnt be thinking too much about this but...
Assuming the spikiest of creatures has a strength score of 18, this gives them a heavy load of 300lbs. We also assume they have to wear a body covering suit of armour (we'll say plate) to fit as many spikes on as possible.
Now, mithral halves the weight of metal items made from it, so a suit of mithral plate (for a medium creature) weighs 25 lbs, so they could potentially carry 275lbs of spikes.
If the spikes are about half the mass of pitons (so big, but not TOO big) and also made of mithral each will have a weight of 1/8 of a lb, so 8 to the lb. Adding that up means said creature can potentially carry (275 x 8 = 2,200) spikes. Assuming you can somehow fit them on the armour that would be how many spikes, though some spikes may well be covered in even more spikes.
That and I doubt youd actually be able to move.
Id say you could have somewhere from 1/2 to 1/4 of that many spikes and still have a reasonable level of mobility.
So...yeah...750 closely, densely packed spikes?
Also yes, Why do you need to know?
