crash1952: a way to install them without GOG Galaxy.
in your library, under the big blue "DOWNLOAD AND INSTALL NOW" button on each gamecard, theres an option to "DOWNLOAD OFFLINE BACKUP GAME INSTALLERS". (edit: see image attached to BreO172's comment above)
any game youve downloaded via galaxy can be moved though, and you should be able to uninstall galaxy without losing them.
as to updates on dosbox games, gog have recently added cloud save support to them - hence the updates. hope that helps.