Your choice of pushing forwards with the sausages as you'd drawn them was the correct choice, and while they are indeed thicker than the reference, that's not something we'd be able to tell without comparing it. It still looks believable otherwise, and that's ultimately our goal here. To create believable 3D structures.

One thing that did jump out at me with your ant - specifically its head construction - was that I feel like you ended up putting down individual lines (2D elements) but without actually considering how they're meant to come together to create complete, self-enclosed 3D forms.

As shown here, I've tried to separate the head into some of the lines you built up around the head mass - I might be wrong about how the red line breaks down, but the blue and purple are my focus - because of the way they're drawn, at least one of them ends up being an addition after the fact, as a single line and not as a complete, self-enclosed form.

Another point of concern is that on the thorax here you appear to be leaving an arbitrary gap between these two additional masses, but there's no actual reason for there to be a gap here. I wouldn't be too worried about this in a normal circumstance, but you have completed Lesson 5 already, and your work there didn't include these arbitrary gaps, and while we did have to work through some revisions, your use of additional masses (specifically the way in which each one's silhouette is meant to be designed, how inward curves and sharp corners occur in response to contact being made with an existing structure) had definitely come along well, but here you seem to have regressed.

I am going to mark this lesson as complete, because by and large you are showing what I want to see in the context of this lesson, but your additional structures (we can see this in the ant's mandibles as well) do not demonstrate that you understand yet how their silhouettes are to be designed intentionally. I'd recommend going through the feedback you received for Lesson 5, and comparing your drawings from the end of that lesson to those here.

You may also want to redo Lesson 5, but ultimately I'm going to leave that to you to decide.

As to your other question, within the context of these lessons, I would indeed recommend that you focus on ball masses when starting both your insects and animals. That's not to say a box isn't sometimes a valid choice, just that this works better in allowing us to focus on a more limited set of concerns at any given time.