To answer your question about proportions before we get started - it's definitely not an area Drawabox focuses on. While we put emphasis on generally investing time into observing your references carefully, it's not so much with concern to proportions (since for our purposes here we can end up with a massive head but as long as the principles of construction are followed well, it'll still be fine for our purposes here), but with paying attention to what forms are present, and identifying what we need to establish early on, and what we can add in later phases.

That said, yes - to both "will it come with mileage over time" and "should I take some course later to better estimate proportions". You will inherently get better with practice, but it's certainly something you may want to take a course on if that is an area you specifically want to improve upon. Remember - what we need to study depends on what it is we're trying to make, and where we are weakest there. It's something where the 50% rule plays a big part, in identifying what our next steps should be. There are some NMA course suggestions here in Lesson 0, although one concept you may want to look up is "negative shapes" in regards to observational drawing. While I can't get into explaining it here, it's a common technique that helps structure what it is you pay attention to, in order to prioritize proportion. Googling it should turn up some useful results.

Onto your homework, your organic intersections are coming along well, especially in how you're drawing the sausage forms arranged in a pile that reflects a believable illusion of gravity. Your cast shadows also demonstrate that you're considering how they're being cast upon curved surfaces, in how you're wrapping them around those structures.

Continuing onto your animal constructions, there's a lot you're doing quite well here, and I can see a lot of attention being paid to the manner in which you're building up your structures - going from simple to complex, making each new structure a complete, self-enclosed form, and so on. There are however some points I can draw your attention to in order to help you continue to make the most out of these exercises.

The first and most important is to do with how we're drawing our additional masses. You're actually already showing a fair bit of consideration to this, but there is definitely room for improvement. The way in which we actually draw the additional masses - their specific shape - is extremely important, because it is this shape design that establishes how it is meant to relate to the existing structure to which it is attaching. There are generally two ways in which a form can be attached to an existing structure. Either it penetrates the existing structure, in which case the relationship between them can be defined by the contour line showing how they intersect, or it wraps around the existing structure, in which case it all falls to the silhouette design.

One thing that helps with the shape here is to think about how the mass would behave when existing first in the void of empty space, on its own. It all comes down to the silhouette of the mass - here, with nothing else to touch it, our mass would exist like a soft ball of meat or clay, made up only of outward curves. A simple circle for a silhouette.

Then, as it presses against an existing structure, the silhouette starts to get more complex. It forms inward curves wherever it makes contact, responding directly to the forms that are present. The silhouette is never random, of course - always changing in response to clear, defined structure. You can see this demonstrated in this diagram.

Now you definitely apply this to a point in some areas, but you are still prone to overcomplicating some of your masses' silhouettes (or at least including complexity that is arbitrary in its nature, rather than being in direct response to existing structures this mass is pressing up against). So for example, take a look at the masses I've drawn on top of this puma. You'll mainly note the very specific placement of inward/outward curves, and where I've specifically chosen not to end up with more prominent corners, using a more gradual curve instead. You'll also notice that I'm putting more emphasis on bringing masses along the back down along the side so they can press up against the hip and shoulder masses where possible - mainly to create more pieces that fit together.

To that point, you tend to build up masses along the legs as separated elements, usually to add a specific bump and impact the silhouette in a particular way. This is a good start, but we can take this even further and yield far more information about our object if we make a point of creating interlocking arrangements of these masses - not just considering one particular bump, but how it's going to integrate with the structures that exist internally within the existing silhouette. Considering these forces us to think about how everything fits together, ultimately making it all more solid and grounded. You can see what I mean here on another student's work.

Since we've talked about the legs, let's take a moment to look at feet. Right now you're kind of trying to tackle the entirety of some of these - mainly paws, like on that same puma - in one step. You'll lay down the overall mass and draw some surface lines to distinguish the toes, but really this should be done with separate forms, in separate stages. We can leverage 'boxy' forms - that is, those with clearly defined corners that help imply the distinction between separate planes without having to specifically draw those internal edges - and then build upon it with yet more boxy forms for each of the toes. I don't imagine that explanation is all that clear, so here's a diagram I'd drawn previously that demonstrates the concept.

Now, while I have definitely pointed out some areas where you can improve upon your animal constructions, I think that you're demonstrating enough comfort and familiarity with form to be able to apply these points on your own. So, I will not require any revisions, and will instead go ahead and mark this lesson as complete.