Pewl,
You're way ahead of the game compared to where I was. I didn't decide to go Rad-Onc until almost 4th-year! Try getting meaningful research in in that time. Of course, here I am writing on this forum as a rad-onc resident.
I think the key is to get involved early. As a first-year medical student, you're already on the right track. In my deprtment, I'm already seeing undergrad volunteers showing up who are interested in Rad-onc. As for getting honors, when it comes to clinicals, enthusiasm beats book knowledge every time.
If you are really gung-ho for getting research experience, you could apply for the Howard Hughes Medical Institute. Basically, you spend a whole year (between 2nd and 3rd yr) at the NCI in Bethesda doing research. I started the application process, but ultimately didn't apply because I didn't want to "waste" a year. As it turns out, I ended up having to apply second time to get into Rad-onc and ended up wasting the year anyway.
Also, don't get scared if your experience at Mallinckrodt is less than a "fun" experience. It does carry the reputation as being a "malignant" program.
As for residency application process, apply to as many programs as you can reasonably afford, making sure you aren't applying to places that don't have an open spot for the year you are applying. Make sure you have a good mix of "big-name" places and "small-name" places. Several programs still do the paper application process; definitely spend the time applying to those as they will generally have a smaller applicant pool. Rank every place you get an interview. I learned the hard way what happens when you don't follow the above advice, at least I was still able to get in on the second try...