I was a bit flippant with this thread because the op does not say why he wants the biggest mod.
Does he want battery life that will last a month?
Does he think his friends will think he is the coolest guy on the block?
Does he want to make videos to show how tough he is?
Does he just want loads of power?
Does he want to turn a tank to molten metal?
Does he just think it would be funny?(I think this is the best reason)
Usually if people are looking for max watts or max amps surely lipo packs are the way to go but that would result in a smaller mod than putting a silly number of 18650s in a box.
Making a box with a huge number of parallel 18650s does not strike me as the hardest build in the world, just pick a number 5? 10? 20? more? and get someone to build it for you. Decide how many £100s of you can spend on batteries and go for that.
Anything less is not really that impressive.