@queensnapdragon Since you're not quite ready to buy yet, there's not much point in my finding good options for you right now—even a week from now, they might be sold out, and something else might be cheaper. I'm happy to help you shop when you are ready though.
For specs, the most important component is the graphics card. The minimum for ultra graphics settings is currently an Nvidia 1650, but since you want to use a lot of custom content and have the budget to aim higher, I wouldn't go below a 1660 (any flavor); a 2060 is a little faster than that. You may well be able to find a reasonably-priced prebuilt system with the even faster 3060, but don't count on it: I'd expect these to sell out quickly if they're on sale at all. If you'd rather go AMD, a 6600 (non-XT) is marginally slower than a 3060, and the higher-numbered 6000-series cards scale up from there. But the speed of anything above a 3060/6600 would be lost on Sims 4, the game just can't use more power than that.
Normally I'd say the processor doesn't really matter, that any CPU that comes with one of the above cards would be more than fine, and that's true as far as it goes. But if you want to squeeze every bit of performance out of the game, look for a processor with high base and boost clock speeds. A CPU will boost when running Sims 4, but it won't quite maintain its max turbo boost, but they fall off by about the same amount, give or take. As an example, an Intel i5-11600K has base and boost clocks of 3.9 and 4.9 GHz, respectively, whereas an i5-10400 has 2.9/4.3. At this level, the performance boost from the faster CPU is small, but again since you have the budget for it, it's probably worth the cost to upgrade.
For memory, you'll want 16 GB, but don't pass up an otherwise excellent option that only has 8: RAM is the easiest and cheapest component to install, with a quality 16 GB kit costing under $60, and a single 8 GB stick even less. For storage, a 512 GB SSD should be more than enough. Extra storage is also easy to add later, but Sims 4 won't need it no matter how much cc you install.
Finally, I would go with a prebuilt system from a company that also does custom builds (Cyberpower, iBuyPower, SkyTech) if possible. They use higher-quality components and have a better overall build quality than the standard sellers, and when there's an issue with the choice components, it's easy to fix or upgrade. If you want to go with a more well-known builder, Asus and Lenovo typically do a better job than Dell or HP.
If you find something you like, feel free to post a link here for a second opinion. And like I said, I'm happy to start looking for deals for you when you're ready.
