My recommendation is that unless there is a compelling reason to do so, then do NOT upgrade to any OS (or any app for that matter).
Unfortunately, almost all of today's developers do not properly design and test updates before a public release, and therefore often have more new bugs than fixes in the release. KM is the rare exception to this trend.
I'm running macOS Mojave, and I'm very happy with it. I see nothing in Catalina that makes me want to upgrade, and a lot of reasons that give me pause.
Of course, compelling reasons could be any of these:
Apple no longer supports your current OS
You have essential apps that require a later OS
A later OS provides features and/or improvements that significantly increase your productivity.
Generally speaking, I never upgrade to a new macOS for at least 6 months after its official public release, and often for at least 12 months. This has served me very well and I have no regrets.
I'd just like to second that point because I don't think it can be stated strongly enough. If computer (macOS) or app stability is critical, the odds are upgraders have little to gain and lots to risk. This is even more true as macOS downgrades are increasingly difficult.
It's probably easiest to just tell oneself that a new version doesn't exist and wait 6 months (or so), as if there were no upgrade path currently available and the new, stable version won't be out for 6 more months. Even then, there may be reasons to stay put, like the deprecation of 32-bit apps mentioned above. In my case, for example, Catalina could be the most stable release ever, but that 32-bit app issue would mean more than $3,000 worth of software I'd need to replace, software I no longer use much but do need to have around. Yes, it's going to be extra expensive when I have to get a new Mac.
On your current Mac, open System Information. In the left-hand sidebar, under Software, select Applications. On the right, you can then sort by clicking the 64-Bit Intel column header, and that will group all the applications which are 32-bit because the listing for them will show as No.
As for FileVault, data security is important to me and a responsibility because of my professional work, so I have long used it. When it was first introduced, the claims were that it slightly slowed the Mac, but it was never anything discernible to me and I don't even know if that remains true as a consideration.
aren't you afraid to be locked out ? there were some rumours of cases years ago and it vaccinated me against even considering it. I have bad memories of being locked out of an extremely important PDF years ago (my fault, I had lost the password).
if you lose the password, are you kaput or are there ways out ?
how do you compare the security value of your computer password vs file vault
By the way, if you bring your mac to the apple store for a repair, you have to ... give your file vault password ! (not your computer password).
I found an app that offers a bit more assistance with 32-bit apps than the System Information approach detailed above. It’s called Go64 and you can find more about it at https://www.stclairsoft.com/Go64/
Apart from identifying 32-bit apps it can also reveal 64-bit apps that have dependencies on 32-bit components and also point you to developers’ websites.
I don’t have any connection with Stclairsoft but I have found Go64 (which is free) very useful.
FileVault password recovery is (optionally) available through an iCloud account. Between that and my memory (for now, at least), I'm not concerned about losing access.
FileVault encrypts the files on a Mac, so access to the files is enabled through your Mac password. In that sense, Apple Store employees only need the Mac password to your account to access your files. While not foolproof, whenever I've had to give my Mac to any Apple repair people, I created a Guest user account for them. But at that point, they have physical access to the machine, so it's not as if that's completely secure.
Here's Apple's support document describing FileVault: