Farm build number will increase only if you will run SharePoint Configuration Wizard after SharePoint cumulative updates(or service pack) installation.
You do not need to run SharePoint Configuration Wizard after installation Windows server updates.
If you will plan to install .Net security patches - be careful with this. It may affect Workflow ...
Regarding this issue while creating dropdown(choice) Column. In column setting select default value by choice and keep that field empty by deleting content in it .so after that while creating item it will show error message as "You can't leave this blank".