High gravity All-grain

Still learning and I think I jumped in too fast but oh well!

Brewed a Three Floyd's Dreadnaught clone yesterday.. 17.5 lbs in grain.. OG was supposed to be 1.084, but i ended up with 1.070... not sure why.

I struggle most with the batch sparging. I think I hit my mash volume and temp just right.. but then I lose control when sparging, never clear on the amount of water needed. According to most calcs I found that I needed 2 quarters per pound of grain.. that's more than my 30 qrt kettle can handle at once.

By 2 quarters, do you mean 2 quarts? I typically calculate how much runoff I expect from my mash, then take the remainder of my desired starting volume and divide by 2 for my two separate sparges. As an example, if you get 2 gallons from your mash, you could assume two separate 2 gallon sparges to net 6 gallons. You should expect basically a 100% return in volume on your sparges; nothing is left to really be absorbed in to the gains or dead spaces after the mash. If you think your sparges are too thick with that much grain, could you try either reducing your mash volume to allow for more sparging or sparging with larger volumes but boiling longer?

I'd hate to try and boil a 5 gallon batch (of anything) in a pot with 2.5 gallons of headroom, get yourself a keggle or bigger pot man.

This way you can sparge until all the sugar is extracted and extend the boil, you can work on dialing in the sparge and extraction as you gain experience.