It looks like you're on the right track there Austen.
Your cam spec looks absolutely fine. I typically use 270 degree cams for 6500rpm operation, and ~300 would be my choice for up to 9k or so. I might be tempted to go a touch longer on the duration if I were venturing about 9k, but it soon becomes a trade-off with low end.
I would leave exhaust specification to an expert. I've been very impressed with Tube Torque in Macclesfield. I suspect you'll end up with 2.5" after the collector, but exhaust design - especially the manifold - is an artform, so I'd rather leave that to an expert (apart from for my own amusement!).
I would use ~45mm throttle bodies. You'd probably say 50mm carbs for that power goal, but since throttle bodies don't have venturis to reduce the diameter (my 40s have 32mm venturis fitted), 45mm should be sufficient. Length...I assume you're referring to the manifold and/or velocity stacks? If so...short is the order of the day for high RPM operation. You can get velocity stacks / ram pipes down to 20mm or so, and I'd be tempted to head in this direction, rather than other extreme of more like 100mm.
Again, I'm not a professional. So if you want definitive answers, I suggest you speak to a race engine builder. Don's suggestion re: touring car engines is a very good one, and one I'd not considered. They were very similar in concept to your engine - 2.0 20v NA 5-pot with ~300bhp.
cheers
James
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