Need some feedback on Case Interview

Start off with taking a step back and just thinking about it logically. All the company wants to see is whether or not you can think. I would also lay this out in Excel because if you're trying to move from a reporting role into corp dev, there might be some doubt as to what your Excel skills are. Here is how I would think about it (numbering these to mirror and tie back to your numbers):

1. I think you are on the right track. You could layer in some assumptions around being able to cross sell the product to individuals not captured by your original market opportunity. For example, let's say that I have no need or interest in an Amazon Alexa. I then buy a Ring doorbell and realize the two integrate. I am now in the market for an Alexa. You could also include some assumptions around different versions of the product and an assumption around cannibalizations. For example, if we assume that Roll Royce sold 1,000 (arbitrary number) vehicles in 2012 when the Phantom was their only vehicle, perhaps they sold 1,200 vehicles in 2013 when they launched the Wraith. Perhaps some of those Wraith purchasers would have purchased the more expensive Phantom if the Wraith were not an option.
2. See above. Maybe layer in an assumption around being able to service your product (e.g. a car dealer modeling out their revenue based on both vehicle sales, but also service, accessories, etc.).
3. Good start here, but you need to get more granular and also demonstrate your knowledge of thinking across functions. I would start with listing out a typical firm's functions (i.e. HR, IT, sales, ops, etc.) and go from there. Maybe HR is not relevant in this scenario. IT might be less so, but think about how new product could affect your IT organization. Do we need a new POS system? Do we need to find a way to integrate new machines into our IT system? Same with sales, ops, etc. Sales will be key to understanding customer needs, while ops will be key to understanding your firm's ability to meet those needs. Throw in some COVID-related supply chain issue questions for good measure.
4. I am not an expert on this one, but like most interview questions, if you word everything as if you were, you'll be fine. I would start by framing this from a quantitative perspective. Cost per interaction, cost per client win, etc. I would then mention how sometimes marketing really is more qualitative. You have an obscure product and have to remind customers that it exists. Or maybe you know marketing works because you can sell your product at above-market prices. Beats by Dre and Bose are great examples of this. Both companies make overpriced headsets. They're not bad per se, but for the same amount of money, you could do much better. Does the average Joe know this? No, because both companies spend a fortune on marketing.