If you haven't found a great need for 2 systems, don't start now. Get a decent laptop, docking station (for external monitors, mouse, KB, charging, etc.) and be done.

If you do go desktop & laptop route, get Dropbox. Move your document folder into dropbox folder and never worry about manual sync'ing. Just make sure your dropbox is sync'ed before you shutdown your machine, or the other unit will be accessing outdated files.