Learn only conversational Mandarin?

yes, always learn how to speak first. enough for travelling. And then, you can learn how to read and write. But speaking always comes first for communication. Simplied is enough, just a little bit difference in writing, speaking is the same.

Thank you for your inquery. For short-term travelling, conversational Mandarin including listening and speaking is good enough. For long-term travelling, you may need to consider more about daily needs, such as grocery shopping in order to save budget. In the case, larning some basic words is beneficial for sure. It also depends on which citiy you plan to stay. People in bigger cities understand English better than in rural places.

About learing simplified or traditional Chinese, there are many aspects to consider, such as the purpose, the duration of learning and devotion, it's not easy to explain the detail without knowing your language level and your thoughts. But I'd love to talk to you more about it.