If the Earth was in Venus's orbit, would it be habitable? If the Earth as-is were moved to Venus's orbit (and Venus removed), would the Earth remain habitable, would it eventually turn into what Venus currently is, or would it turn into something else?

I'm mainly wondering which characteristics of Venus (hot, no magnetic shielding, etc) are the result of how it is composed compared to it's proximity to the sun.

Similar question: If Venus and Mars changed places, would we then have 3 habitable planets?
A planet's environment is a complex interplay of factors.  If you dramatically change the insolation of a planet, it becomes very difficult to predict how the other factors which influence the planet's environment will respond.

Venus, for example, seems locked into its high-CO2 environment (which makes its surface hot) because its surface is too hot to allow for the formation of carbonates.  Even if it had water (also needed for the formation of carbonates), it would be continuously boiled away from the surface.  

All planets - Earth, Mars, and Venus included - have their temperatures influenced by their albedo.  Albedos of planets are often strongly correlated with cloud cover.  Cloud cover generally increases as a wet planet warms, reflecting more light.  But atmospheric composition can overcome this balance, as in the case with Venus, which has a very high albedo but is still swelteringly hot on the surface.

Even if you get rid of the feedback factors like water and carbon dioxide, the planets have very different nitrogen levels - Venus at about 2 1/2 times that of Earth (enough to cause mild nitrogen narcosis on its own), and Mars almost nothing.  Really, Mars in Venus's position would be in a terrible state - it's been so stripped of its atmosphere even as far from the sun as it is, it would be all the more stripped being much closer to the sun.  Over geological timescales it'd become highly water stripped as well, as it'd be much easier for water to enter a gas phase, and the solar wind can very effectively strip water planets even as large as Venus, let alone Mars.

Venus in Mars' position would probably fare much better.  But it's difficult to say exactly how much.  Given that we can't say with great confidence exactly what set in motion the path that led to its current state today (thicker, more viscous lithosphere preventing crustal overturn? cause or consequence?), it's hard to say whether that would have happened had it been in Mars' orbit.  One curiosity if you took today's Venus and moved it to Mars' position: you may well cause an atmospheric collapse to a supercritical state. It's been theorized that even in its current orbit that's happened before (temperature runs counter to the formation of supercritical fluids).