Hello @tausendSASsa,
not sure if you are speaking on a PC or a Server deployment, but, it really does not matter anyway, the answers would be the same in both scenarios. Since you speak about sasadm@saspw account, I will understand you are talking about a server.
No, you don't have to chose different directories, specially if the maintenance level is the same.
It is more up to you, if you want them to be a same environment, or different/separate environments.
Different Levels are normally used to virtually separate deployment tiers (metadata - compute - web - clients) or DTAP levels (development, production, etc)
If you select the same configuration level, you won't need new passwords (except, for new accounts), you will need to type in the same passwords as on your initial deployment, since you are just adding products. If you select different configuration folders/levels, you will be prompted for the host and port of your metadata server, and if it is going to be a new one, you might need to select new accounts and passwords.