Is undersea farming a possibility? If not, why not?
Yes, but we have to stop dumping mercury, et al into it. Also, we'd have to determine who has the right to cultivate where - should we sell the plots outright and 'own' a piece of the sea bottom, or should we (the nation) just rent them to those who wish to farm there.
If yes, then is it possible to create bio fuels from the crops that can be produced under the oceans? If Not, why not?
Yes. Algae has a very high yield for biodiesel. But why bother with the ocean, when we can do it, in much better controlled environments, on land. Link
Apparently we can replace the gas and diesel used for transport in this country by building algae ponds on 15,000 square miles of land (0.5% of the Continental US's land area).
If yes, how would we best fund the start up of these projects, with and eye on promoting private business ventures over government ones?
By having the US Gov't lease plots of seabed to private ventures. Additionally, a carbon tax on nonrenewable carbon-based fuels would make such a venture more economically attractive. To maintain a healthy economy (and demand for energy) the total revenue from the tax should be paid as a dividend to all US Citizen's -- Trickle UP economics.
Would public support be enough to counter the political opposition from Oil companies and the like?
I'm not sure anything can counter political opposition from Oil Companies for the next 3 years.
What negative environmental implications could there be with undersea farming? Assuming there would be some, would the negatives in this case outweigh the potential benefits?
There's always negatives. I *Think* that it might lead to a push for higher environmental protections - as you need a healthy environment to grow things, even underwater.