If he got it after PGY1, he must have gotten it in Pharmacotherapy. That is the ONLY one of eight that only requires PGY1. Everything else need a few years before you can sit for it even after a PGY1 residency. I think, besides nuclear, all the rest lets you sit for it after a PGY2 (in the specialty). Anyway, so in theory, I think a residency is equivalent to experience (it is debatable as to whether or not it is true in practice). Without any residency, you have to put in 3 to 4 years in the field in order to get board certification. Look into it.
Anyway, I think it is smart to think about residency in your P2 year. I didn't think about residency at all. I only started thinking about it after I graduated and got licensed. LOL.
However, I personally don't think you know enough about any field to pick the field you want to specialize. I think that is the point of PGY1 (and even rotations, try getting a rotation in something you might enjoy for your P4 year). If you really want to specialize, nowadays, yes it is probably best to do a residency because it is difficult to get into a clinical setting without it (not impossible, but very difficult).
Now, to address your oncology pharmacist question, fortunately for me, I networked a LOT and I just got a position as an oncology pharmacist without a residency. I think it is a great field. I am still new but I will try to answer any questions you may have. I do plan on staying at least four years because I do want to get board certified but hopefully, I will be doing this until I retire. In regards to patent attorney, you are talking to the right person. This is something that I researched myself. What are your exact questions about it?
To be completely honest though, you need to work on completing your degree first. While you are completing the degree, my only advice to you is network, network, network. LOL. Thinking about what you want to specialize in 4 years from where you are sitting is kinda fruitless because you never know what field you will end up enjoying. Network and pass your classes. In your P3 year, truly sit down and plan your rotations out. Then, in P4 year, figure out what you like/apply for a PGY1 residency. That is it. All the advice I got for you.
Sorry about bad grammar. Really, really sleepy.