Before I install owncloud on a host, can anybody tell me if two way sync is working on the android client?
two way sync is currently working for single files (not for folders) which you need to mark as "keep in sync" manually.
There are alternatives like "Foldersync" which provides additionally functionality
Does Foldersync work with remotely hosted OwnCloud installation? Or does that only work if I have OwnCloud installed on a local server?
I don't think that Foldersync cares where oC is installed. Thats just a 3rdparty app accessing a WebDAV server. If you want to make sure google around how Foldersync is working.