Keep in mind that the more sugar you add, the less body you'll have in the final beer. It would taste pretty watery if it's a lot of sugar. I wouldn't go with more than a few pounds at most.
There's nothing wrong with adding sugar to an IPA, I use 1.5lbs of corn sugar in my IIPA, but I would try to make most of your batch with grain. If you're thinking about doing this because of mash tun size, then I'd suggest using a late addition of extract instead of a bunch of sugars.
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Another HERMS rig...