Leave it to NJ to have a law for pretty much everything.
Depends on what state you're in, but I think architect is the way to go. Do a Google search for terms like "Building Design Law", "concurrent practice", "architect", "engineer", "closely allied professional" for your state. In NJ, it's clearly delineated what architects can and can't do, and what engineers can and can't do, for every building classification (NJ's law uses the BOCA terminology). As a licensed engineer, I can't seal plans for a new structure in the R classification (residential), period, so new construction R class is considered a prohibited classification for me (but not for architects). But I can seal plans for "engineering systems" (beams, HVAC, etc) within the R classification, and for designs "of an incidental use" within the R classification. But there are area thresholds I have to abide by. Such as, I can't seal plans for a tear down, but I can for an addition if it's under the area threshold. Decks, gazebos, foundation repairs, roof mods, beams, openings, these are also considered "incidental use" projects, subject to certain conditions.
Talk to the town and your insurance company. They'll probably know which professional is needed before you finish your sentence. The insurer will also want to make sure the designer carries professional liability insurance. But with all that said, from the scope you listed, I'll bet you a sandwich it'll be an archy that has to seal the plans (and an engineer will probably be part of the process in some fashion - site plan, foundation, etc).
