Well I haven't used Plasma Mobile or any of the apps you've mentioned, so it'd be nice to see what it all looks like! (and I don't have a device I can try it on either, unless I can get it working with Termux + Termux-X11?)
I also had it ignore the mysterious “DELETED” format Firefox sends that is likely a remnant from the XDnd specification. The latter fixes dropping an image to the desktop to set it as a wallpaper
That really depends on your needs, and the Linux distro you’re using. Generally speaking, the greater your requirements (and therefore usage), the more finicky an OS gets.
I switched my non-techy Mum and Dad over to Linux over a decade ago (Xubuntu previously, now Zorin) and in all this time, I can count on one hand the number of times they called about an issue. The entire motivation to switch them over was because Windows was so unstable and would either tend to break after an update, or get infected by malware or something, and I got tired of being the IT guy for them and having to constantly fix it. I reasoned that Linux would be a good candidate for them because they have very simple requirements - they mainly just use a browser foe the most part, work with documents occasionally and do a printout once in a while, like for flight tickets and stuff. More than a decade later, my reasoning was proven right, and I’m glad it’s been working so well. Linux was the very definition of “just working”, at least for my parents.
I disagree, try running KDE on a 4th Gen i3 and compare it vs a modern system, the performance difference is pretty night-and-day. It’s not exactly unusable or anything, but it just doesn’t feel snappy and responsive, when compared to a lightweight DE on the same hardware.
For such an old system, your DE matters more than anything. I’d recommend XFCE, or even LXQT. Definitely upgrade your RAM though, that’ll give it a nice boost - DDR3 should be pretty cheap now. Any cheap SSD should be a big improvement as well.
I’ve got Zorin installed on my mum’s PC (which is just as old as yours), and it works really well, even on a regular HDD.
NZ here, I use it for online purchases. Credit cards have the advantage of extra fraud protection, as well as having a safety net of being able to do a chargeback in case the seller does fraud or something. I don’t need to pay any interest on it either because I make use of the interest free days. I have a direct debit set up so the bill gets cleared on its own every month, so I don’t forget and accidentally pay interest or something.