1) Database: Depends on which db you were using. If you were using the H2 db then it was in the razuna folder and is lost unless you have a backup. If some other db then you will still have the db information intact
2) Assets storage: Unless you specified a storage outside of the razuna folder this information is lost and can not be easily re-created.
Your best bet would really be to start afresh if you did not have too many files.
With Razuna 1.6.2 we've had an issue with search processes running too long. Thus I highly recommend to set it to 5-10 minutes. With Razuna 1.6.5 you are good with 2 minutes. Just wait another week and then upgrade ;-)
The "master" branch on Github is always a released version and will run without issues (apart from bugs that we might not have caught). We do have a "develop" branch and other sub-branches where we do our development.
Nevertheless, if you don't know what you doing or want to be "safe", I would recommend to stick with the official released version. Thought, you can also simply checkout the version tag from Github and then you are good, too.