There were not many changes between alpha3 and alpha 4, but it’s recommended to update always from the previous version to the latest. In any case, if you don’t want to lose any configuration, I’d suggest you create configuration backup in Foris and/or create a snapshot. Snapshots are created before and after the update, but they are regularly deleted. More details in our documentation for Schnapps.
About LXC, we’ll see. It was already discussed here: Why the "Print server" package is now marked as OBSOLETE? and cross-link reference to issue in OpenWrt packages: https://github.com/openwrt/packages/issues/7694.