Is basically logistically impossible though, so there's that.
Would absolutely require congressional blessing unless he plans to find tens of billions of dollars in the couch cushions. (and no, the idea that Mexicans are going to pay for it is both likely unconstitutional and would also require congressional action anyway)
Blatantly unconstitutional, as you would be ex post facto removing citizenship from millions of Americans. As for future 'anchor babies', he would be relying on a fairly radical reinterpretation of the 14th amendment, even if he could get Congress to sign off. Let's put that in the 'very unlikely' bucket.
Funny thing, comprehensive immigration reform passed the Senate (in a bipartisan fashion no less!) and Obama said he would sign it. House Republicans never bothered to take it up for a vote. Most likely because Boehner was afraid enough Democrats and Republicans would join together to pass it.
Trump's 'plan' is a ridiculous fantasy that falls apart as soon as you even try to apply it to reality. It's unhinged ranting for those who like ranting more than they like actual policies. If that works for some people, I guess that's just a sad statement about politics in the US.