Task bar became non functional. Easiest reinstall from scratch of 19.1.

When it comes to Mint, I honestly don't see why you would feel the need to hold back. Mint 20.1 is based on Ubuntu 20.04, which is almost a year old. That means that most software is on a year old versions, with a year of bugfixes and security fixes applied.

I suppose the only thing that might be less tested would be the software that the Mint people make themselves, which is just the Cinnamon desktop. But all the core components that your computer actually runs on is well tested. Even the repositories that Mint use is Ubuntu's software repositories. Mint only has one "Mint" repo which contains the cinnamon desktop, and some other software.

So in my opinion at least, there is no need to worry about a Mint update. Every new Mint release, is already an old Ubuntu release, especially when you come to the dot releases, as in 19.1 or 20.1.

Now that I honestly don't know. I suppose just check the Mint website for the recommended way to do it. I don't think there should be a problem with upgrading, but you might want to do some cleanup after. Like removing unneeded software, getting rid of old kernel versions still taking up space.

I am personally not that familiar with the graphical installers anymore, but I seem to recall there being an "advanced" mode at the partitioning step. At this point I think you should be able to set it up so that your HDD is mounted on /home. But I just want to point out that I don't know what the installer does, and if it will touch the data on your /home partition. I would backup the data on your /home, just as a safety measure. But I don't think it needs to do that unless you specifically tell it to format this drive. Still, copy over any important data to an external drive first so you don't lose anything.

Ah, yes. Windows. The horror!