1. you don't actually have FSD, you have an FSD compatible tesla. I bought my car in 2020 but the first real version of FSD I received was V10.12.2 (part of 2022.12.3.20) in June of 2022. What you have is basically Enhanced Autopilot (so lane change when you signal and Navigate on Autopilot) and summon. Don't know if your summon still works. I used to be able to use mine to back in tight in my parking spot but I can't do that not because of an update that requires the car to be able to see a satellite and I park underground.)
2. if you update you will get stuff and you will lose stuff. You'll have to do all the reading to figure out what but if your radar is still working, it will stop. On the other hand, you'll be pleased to know the fart sounds still work! Your user interface will change dramatically. I can't remember if you still have your defrost button and wipers on the main screen automatically. I had to wait months for the option to return them. If you are happy with how your wipers work on auto DO NOT update. Your maps would be updated which could be a good thing. On the other hand, they don't seem all that well integrated into V12.3.x and it will often completely ignore the speed signs and speed up/slow down to the number that corresponds with the highway number. This means I can't use FSD for 2/3 of my 3 hour drive 2x per month.
3. if you have been so incurious as to not update your car to at least see what each version of FSD is like (they were all bad to various degrees) why would you be considering updating now? V12.3.x of FSD(s) may be the closest version to not sucking completely, but if your logic was you were only going to update when your car when it was truly autonomous, this is not the time to update.
4. yes, the nags are worse, both in FSD and AP (don't know if you can cover the camera or not but I think I read somewhere that if you do, you get more frequent wheel nags.) We don't find them intolerable and have never had a strike, let alone been locked out, but they are definitely worse than before the December 2023 updates.
You sound like someone completely happy using AP illegally (i.e. with a defeat device) and pretending you own an autonomous car. You will lose that if you upgrade.