Sims 3 is certainly compatible with high-end hardware, it's just not going to use all that extra power. There's no practical difference, either good or bad, once you get past a certain level. So if you're not going to play other demanding games, you don't need to spend the extra money, but it wouldn't be a bad thing to have a stronger system than necessary.
As far as framerates go, 75 isn't better than 60 unless you can tell the difference between 75 and 60. The question was more whether you want your graphics card to be able to maintain high fps, for example 120 or 144, rather than 60 or 75. But the refresh rate of your current screen is 60 Hz, so you may not mind similar fps.
Since you want to play at 2560x1440, I don't think you should go lower than an Nvidia 1660 (any variation). An AMD 5600 XT is somewhat faster, and an Nvidia 2060 is a bit faster than that. While you could certainly play just fine with a slower card, for example an Nvidia 1650 or an AMD 5500 XT, having a faster card buffers against the framerate drops that Sims 3 will produce on any system. To that end, a 1660 should be more than fine. But if you see a build with a 2060 for only a bit more money, it would be a good purchase.
Processors can be complicated, but any new system that has one of the above graphics cards should also have a CPU that's more than good enough for Sims 3. You will probably want at least 16 GB RAM at some point, but it's cheap and easy to install more whenever you want. So if a system you otherwise like a lot only has 8 GB installed, it's fine to get it and upgrade the memory yourself. You'll probably want a solid state drive of at least 500 GB, but Sims 3 won't really need even half of that, so you don't need more storage unless it's for other purposes. The difference between playing Sims 3 on an SSD vs. an HDD (mechanical drive) is significant though.
So, to summarize:
- Graphics card: Nvidia GTX 1660 < AMD 5600 XT < Nvidia RTX 2060
- Processor: Probably whatever comes with the GPU is fine
- Memory: 16 GB is nice, 8 GB is enough, you can upgrade yourself
- Storage: 500 GB SSD storage for Sims 3, Windows, and basic apps
For the monitor, there are always a number of good options, although getting one with a 2560x1440 resolution cuts down the list and also drives up the price. IPS/PLS panels are the highest quality, followed by VA/SVA; don't get a TN panel if you can avoid it. And figure out the size you want before you start shopping; it makes things a lot easier.
I'm not sure I'd know where to shop for you, but if you have any specific stores you'd like me to check out, feel free to link them. Or you can link individual builds you're considering. The same goes for the monitor, although I could link you some good options you'd find in the U.S. if you'd like a place to start.