Basically, the advantages of having a home program are what you nicely articulated.
1. If you have a home residency program, it means that it has ACGME minimum qualifications for training residents which includes basic requirements for research and educational infrastructure.
2. You definitely have a better shot at matching with your home program since you can start and begin to cultivate your relationship early in med school.
3. If you have a home program, then you will likely have prominent faculty who can write you nice LORs and help you network with other Rad Onc programs.
4. Perhaps most importantly, you will have a program director you can interact with directly. (S)He can give you excellent advice about your chances of matching and how to improve them.
To the OP, I would concur that starting research early in the year is worthwhile. Though it is far too late to present anything at ASTRO, there are other national meetings which you could shoot for.