Please read the post on my signature if you want something very well explained, with (almost) no technical term.
And since you are on ubuntu 19.10, please read this thread as well. It does have a lot of technical terms though.

For the rest of your questions.

There are no suggestions to install chromium, but chromium ffmpeg codecs, which is something completely different. The first is a full blown web browser and uses 200+MB of space, the second is a subset of its libraries and uses ~5MB of space. The "why" it is suggested to install them is explained on my post.

If you think that opera is messed up because of the files from your previous installation, the best thing you can do is export its bookmarks, delete /home/username/.config/opera completely and start fresh. Opera will be reverted to its stock settings, with no extensions, with no leftovers from last time. Stored asswords, settings, etc will also be deleted, so make sure you know them.

Finally, python has nothing to do with opera. It is not used to build it, it is not used to run it, it is not required by any extension (as far as I know). Long story short, opera's connection to python is non existant.