Q1) LiveCycle uses an XML based technology to build forms (called XFA), while Acroforms is an extension of the core PDF standard. XFA has more features than Acroforms at this time. For your purposes, either will work.
Q2) I believe the Import / Export restriction applies equally to Acroforms and XFA forms. Using Acrobat lifts these restrictions.
Q3) ES4 is the last version of LiveCycle. The new product is called AEM. You can download a trial using these instructions: