1). you can update it with zune without any problem, and don´t be fear you don´t gonna lose the unlock you gonna be able after update of do everything you can do now like side load xap´s and modify the registry
2). yes, after of install nokia driver.cab you can use the nokia apps, but you have to change the samsung market for the nokia one, you can do it with this app
http://xdaforums.com/showthread.php?t=2369123, some of nokia app also require to change the device name for a nokia lumia ir order to work.