Hi Robin, This is not a bad start! Starting your education in form by working solely from photographs (I imagine you are not at the safari park!) is challenging and unintuitive. If you want to better at understanding how to draw forms in perspective, the best way is to first build an understanding of them in real life. Get your hands on some objects that approximate the basic forms. You could use a wooden block or rubik's cube as a cube, a soda can as a cylinder, etc. Spend time rotating these in space at arm's length and just looking at the shapes that they make. What section is pointed towards you? What section is pointed away? What is the severity of the tilt Are you seeing it from above or below? While you are observing this, try to imagine in your head how you would draw that basic form. Build intuition through observation! Once you feel comfortable with these basic forms, start observing other things, apply that intuition and do it all the time! You will begin to get a better intuition for this stuff, how shapes need to sit in space in the 2d plane we draw on. The best artist I know are always observing the real world in these kinds of ways, even when they're not drawing. Hope this helps some.

Learning is like putting together a jigsaw, once you place a piece, you should keep trying to build on it, eventually we get the whole picture. You don't want to fixate on forms forever, other material will help build your knowledge of basic forms further, such as light and shadow, perspective even gesture. If you feel a necessary need to go back, then go back for a short while then continue to push forward. I'm no expert on art or teaching, but I've learnt after trying to self teach a lot, that pushing forward always beats going back.

I think it depends on what you want to do, if you're doing this study for accuracy and for a clean result, and using a perspective grid makes it easier for you, go ahead! If you want to learn how to break down subjects into basic forms intuitively, practicing drawing basic forms and shapes is a great start. Then, you can try doing a simple study first using a perspective grid and then try it without, intuitively drawing the forms.

Drawing basic forms is not as intuitive as it might seem at first glance. It looks simple, but there is a lot of nuance to it. A lot of art books and courses don't pay enough attention to really nailing down how to do boxes and cylinders correctly, and if you move forward without a solid understanding of those things, it will plague your drawings. I was thinking about posting some threads to help with this very thing. Let me know if you're interested.