I went to remove thunderbird and it wants to remove package called mint-meta-gnome and mint-meta-main. Will this screw my system up, and if so, how can I remove thunderbird without removing these packages?
They are just meta packages... i.e. they don't contain anything and just depend on a whole bunch of packages... so you can get a standard mint main edition setup by installing one package, for example.
You can remove meta packages without any bad effects.