Virtual Machine and Container Questions

I just recently discovered that I can install any OS I want through the virt-manager software. This means that I don't need to switch computers or partitions just to use one or two features of another OS. However, I am wondering if there are any security concerns with doing this... For example, if I am using Windows XP in VM, can something compromise my host system? Are there any things I should look into to harden the security somewhere? I have heard of Docker and containers, but I don't really know much about them. Do I need to "dockerize" things in this case?

I'd appreciate any tips or advice on where to look to get on the right path to learning more about this stuff, especially in as "Libre" as possible way.