I went for a company that I used to work for, to try and counter-act the fact that the Partner will be vastly more knowledgeable. Whoever you do your presentation on the Partner will ask you questions, one or two of them may be tricky but they are not trying to catch you out - purely looking to see if you have some reasonable business knowledge and can make sound suggestions for improvement. More importantly, you will need to be able to justify your decisions.
And yes, it is very important to suggest where KPMG can help! This is where you demonstrate that you have researched the entire company, not just the service line you have applied for. You don’t need details, just an idea of what services KPMG offers and how they could be of use for the company you present. Again, the Partner isn’t going to try to catch you out!