If your long-term goal is strongman, work on strength and athleticism now, along with hypertrophy. Hypertrophy blocks (essentially bodybuilding training) and accessory work done like a bodybuilder are definitely useful for strongman as well, but don’t neglect strength work early. It will make your long-term goals more difficult to reach if you do. And trust me, strongman-training can pack on muscle. You won’t have to worry about that, lol.
I’d look into the stuff Kalle Beck has on starting strongman (don’t know if I can link to it). He’s got good programs for what your goals are. I know that he believes in a lot of bodybuilding style training for a beginning strongman.
5/3/1 is also appropriate for building a strength base, just don’t neglect the conditioning work. It’s important.
you’re going to have to do things you aren’t used to, in order to become something you haven’t been before. Don’t eat like you used to. Don’t train like you used to. Train and eat like the people who have had success before you. I can promise you, you won’t find a lot of strongmen out there eating an orange with some pea milk for breakfast.