Well, let's try to address all here...
1. You can only have DVS on the ESX servers with Enterprise Plus licenses. Any other license does not support DVS. Anyway, you can create a DVS where only the Enterprise Plus licensed hosts participate.
2. The DVS facilitates the network management when you have a lot os ESX servers - if you need to create/change a portgroup, you don't need to go on every ESX server on your cluster/DC, the configuration is "replicated".
3. The hosts does not need to have the same number of uplinks, but they *should* have the same number of uplinks dedicated to the DVS, in order to avoid configuration problems (if you force a dvPortGroup do use a spacific dvUplink, and one of the hosts does not have nics on this dvUplink, the communication will fail when a VM is on this faulty ESX).
4. Yf you have spare nics on your system,you can attach them to the DVS and simply change the portgroup configuration on each VM (there are wizards that can help you doing this on all VMs at the same time for a given portgroup). After that, you can reacomodate the nics on the DVSs.
5. DVS are hell for troubleshooting if you get in the case some problem happens with uplinks, and more if the ESX management are attached to the DVS.
Hope this helps to understand better DVS 