I just started a rewatch yesterday, but I'm on Ep 04.

For 01/02, I definitely agree with the hard sci-fi and casting. The first few episodes seemed a little slow-burn to me the first time I watched them, but on a re-watch, I'm noticing a lot of elements and call-forwards to things that are important later.

Can someone explain the reason for Holden's wrench to go flying?

I believe their shuttle was under (light) thrust at the time since they had a limited supply of air and needed to reach a shipping lane (or as close to as they could manage) before running out. He just let go of it expecting it to float there but forgot they were under thrust - either due to the stress of the situation or because he wasn't as practiced at EVAs as Amos.