the answer is "it depends". Yes, its perfectly ok to follow Cade's strategy and create few ( 2-3 component diagrams).
Normally for each unique flow, there would be 1-2 VO's involved. You may not write the entire details of each VO just a mention would be sufficient.
Yes, its best to put non-functional "good-to-have" features like SSL in ur assumption section.
Yes, those 4 use cases are the ones u'll be graded on. If you feel additional use cases will support ur understanding and/or architecture, go ahead and depict it. But as for component diagram is concerned, they all will follow standard typical artifacts for each unique flow( ie view, controller, helper, validator etc).I depicted additional use cases if any in sequence diagrams to depict pre/post conditions w.r.t other use cases and left the component diagram from getting cluttered.
Yes, alternate processes are important and best represented in sequence diagram and/or in the assumption section.
Hope this helps.
Sankha Subhra Das