Virtual machines to install for OS+Ubuntu+Windows
Yes it's possible. You don't need to install multiple virtualization software to run multiple virtualized systems.

You can use one virtualization software (VMware, Parallels or VirtualBox for example) to run multiple virtual machines at the same time.

You can edit the Virtual Machines. 



You can change the amount of memory and the number of cores used by each virtual machine among other things, but it requires shutting down the VM you will edit.



For non Bootcamp virtual machines, you can also change the settings of virtual hard drives by creating new drives, removing existing ones or even resizing existing virtual hard drives (which are just files on your hard drive).





Getting the best of both worlds.

I would recommend you install Windows in Bootcamp first. Then back in Mac OS you create your Windows virtual machine from the bootcamp install. Follow this procedure.

This way you will be able to either launch Windows from Mac OS and run both systems at the same time and restart your computer to boot into Windows natively for better performance (for video games or power hungry applications).