You can easily install multiple versions of WL studio on 1 machine, just use a fresh install of Eclipse for each version. Creating separate workspaces inside of eclipse will have the same version of WL across all workspaces so you will need multiple Eclipse instances to accomplish this. In regards to your Android SDK question you can point each eclipse instance to the same Android SDK, but you will need to install the android tools on each version in order to work properly.
Please make sure you are running the latest 6.0.0.x ifix when attempting to run at the same time as some issues were resolved in this version. If you are an IBM WL customer please request the latest fix pack containing this fix.