Sounds like a tasty beer! I brewed a batch with rooibos this past weekend. Used about 50% more tea than your recipe has, plus I may use some at bottling with the priming sugar depending on how much aroma is left.
As far as the lemon, I suggest using the zest in secondary, basically dry hopping it, because in the boil you'll lose the aroma it adds and you're left with bitterness that you hops will take care of. You may also think about using a hop that would lean towards lemon (Cascade, Amarillo) rather than Citra's more tropical notes, at least for dry hopping. Citra is great, but maybe not right if you're going for "lemonade". On the other hand, you could pick hops to complement the earthy notes of the rooibos. I used Willamette for mine, but there are plenty of others along those lines.
Lemon pulp/juice directly in to the wort will be STRONG, so don't get too carried away. Don't get me wrong, it was great, just stick on the low side and add more in secondary if it's not strong enough.
Haven't brewed with brown sugar, but thinking it will add some dark flavors from the molasses. May consider a lighter sugar to keep it summer-y, or leaving it out. 7% is high for what I think of as a summer beer.