No, I wouldn't multiply spices and (especially) salt by 5. I'm guessing you'll need less. I say that from personal experience in doubling and tripling other recipes, but I imagine my experience would extend to Indian cooking, as well. I was taught that in
doubling recipes, to use 1+1/2 times the amount of spices and salt, and then to taste and add more as needed. Of course, that presumes you know the taste you're looking for, and will be able to adjust accordingly.

Another point, probably not worth mentioning, but the sauce will evaporate at a different rate from a 50-ltr cauldron than from the usual household pot. That will change the timing, and, perhaps, the taste. Again, you'll have to know the final texture and taste you're aiming for.