In general yes:
At the core of the x86 application side of things win10 is EXTREMELY similar to winVista/7/8/8.1 and not much is planned to change on this front, so x86 apps will move over quite nicely. There are probably going to be a few graphics issues when they release the new version of DirectX (11?) soon, but those will mostly be driver issues that will be ironed out in time, and is more on the GPU manufacturer to support rather than MS directly.
win10 is also backwards compatible with the older metro/modern APIs so those older apps will work (granted many seem rather broken in the current build, but I am sure that is a temp issue), though they will probably not launch/run as quickly and efficiently as apps built on the newer universal/Windows App APIs.
As for syncing settings like wallpapers, IE favorites/settings, etc. the answer right now is yes, they do work, even on a fresh install when you sign in using your MS acct instead of a local acct. On top of that there is no reason to believe they will change their settings sync engine, so it should work through the final build.
Think of win10 as a new UI, a new browser, cleanup of legacy things like Control Panel and confusing settings locaitons and menus, a new GPU engine, and an expanded Metro API set. The core OS is largely being left alone, so most things that work now should work going forward.