Can I have multiple surveys ongoing at the same time?

Yes, you can run multiple surveys in parallel, for example a pulse and a yearly survey. 

When running multiple surveys in parallel the survey questions will merge for the user, i.e., opening either one of the survey invites (links) you will get all the questions for each survey at the same time. The questions will be combined to avoid duplication. Meaning the user will answer a question once but the answer will be related to all relevant survey send outs that require the answer for this question from the user.