The tracks are all individual, so to upgrade to VCDX6, you will need to take the VCAP6 Design exam in that track. For example, if you are a VCDX5-DCV, regardless of how many other VCDXs you hold, you will need to pass the VCAP6-DCV Design exam to upgrade to VCDX-DCV 2021.

There are two separate fees: An Application Fee of $995 USD is collected when you have submitted a complete application package. If the application is accepted for a defense before the VCDX Panel, a Defense Fee of $3000 USD will be due. Fees are subject to change. 

Any and all costs related to traveling to a design defense are the candidate's responsibility.

No, it will not. The presentation is a tool to refer to when answering questions from the panelists, rather than to use as a full presentation. Although you will be given a few minutes to provide an overview, be prepared to start answering questions at any time. Use your presentation as an indexed tool to quickly jump to slides that will help answer specific questions. Since the panelists have reviewed the design already, they will already know much of what you are presenting, and they want to ensure there is time to answer questions they have. Overall, it is better to answer the questions than to go slide by slide through the presentation.