Before I start, I have worked in both Investment Banking and Consulting, therefore have a good view on the differences across those two industries.
Both industries are quite similar in the type of people it attracts intelligent, analytical, huge drive/ambition, eager to learn, problem solvers.
However, the industries have also fast difference in the type of work, working culture (hours/expectations) etc.
Key platforms are Wall Street Oasis, Street of Walls and my favourite for building knowledge (not prepping interview) is Corporate Finance Institute.
Key is to ask some bankers at the place you are applying some insights and materials they might have.
Important to know that for interviews in investment banking it is rather improving your knowledge on the key topics (accouting, modelling) / while for consulting it is the way you think and solve problems you need to train. The latter is off course way more complex.
Lastly, for Why IB? This is really a personal process that you need to grow. The problem with this question is that people don't have it figured out and therefore you hear during interviews quite similar / boring / in-personal answers.
In general the key drivers for people to join investment banking is exposure to highly strategic topic at a young age, fast learning curve in early stage of career, developing their problem solving/analytical skills, being surrounded by extremely smart group of people and learning the basics to become a future investor.
But work hard to try to find an answer that is truly your own if you want to stand out to the interviewer; otherwise he might just zone-out while he earns person #10 on the super day with the same three answers without personalizing. Even if you use the examples above, connect it with your personal story why it is important for you.