In the past, I've said "for bigger triceps, learn from powerlifters; for bigger biceps, learn from bodybuilders." This explains why you've been doing—and will continue doing—close-grip bench press variations every arms day throughout Built by Science. For my money, there's nothing better to build upper-arm mass, especially if you follow it up with overhead triceps isolation work.
But at the end of the day, I also get that biceps and abs are how many people will gauge the success of a program. This week, you can finally pick up the EZ-bar and curl to your heart's content. In addition to biceps curls, you'll perform reverse-grip EZ-bar preacher curls, which are great for forearm development. Expect to lower the weight between the two variations, because the reverse-grip curl is far more of an isolation movement than a regular curl.
If you've watched the abs overview video, you know that I believe core training isn't just about moving your trunk a certain way. It's about by forcing your core muscles to resist movement in the form of extension, rotation, and flexion. If this is new to you, definitely watch the video again and learn how to perform the exercises below—especially the TRX fallout and dead bug.
The TRX fallout is like an ab-roller hanging in space—and it's just as difficult as that sounds. You'll need maximal tension in order to pull yourself back up from the front of the movement. But in exchange, you'll be giving your obliques and six-pack muscles the stimulus they need to grow.