I’ve neither encountered any problems with 10.4.3 nor heard of any user problems specific to 10.4.3. Of course, as always when installing OS updates or security updates, first make certain that your system and disk are in good working order – and run permissions repair both before and after the update. Of course, after every update release, one sees on the Internet reports of all sorts of disasters encountered by some users. In my opinion, those problems generally result from updating a computer that has preexisting disk and system problems.
I’m happy with 10.4.3 and recommend it.
There are no risks in using multiple databases. (Just make sure you don’t run low on free disk space – allow at least 10% to 15% of your drive capacity as free space. Apple engineers recommend this for all applications, not just DT Pro.)
I’m not using Workspaces on my current project databases, but have not heard of any user problems, nor had any when I did some tests.