1. If it is a vector symbol, referencing no external image file, then yes, it will be contained entirely within the .fcw file. If it uses any kind of images, either an image for the symbol itself, or a raster fill, then it will be dependent on that image.
2. For a pure vector symbol, yes, no problem at all. Additionally, if it do reference fill styles, but those fill styles are official CC3+ fills (including addons), then yes as well. Problem is only if you have brought in your own custom image to use for the fill.

One of the reasons it is bad for CC3+ is that a higher resolution monitor simply have more pixels. CC3+ needs to render a new image to present on screen from the vector data every time things change, and rendering a 4K image takes 4 times as much cpu time as rendering a 1080p one. Since it is already working as fast as it can, that basically translates to 4 times as long in actual time as well, so a 4K monitor is simply slower to work on. This will be more or less true for any vector-based application, while raster-based editors works differently, and mostly just need a bit more of memory.

The net effect is offset by the power of your CPU, so the more powerful the CPU, the less of an actual impact a high-res monitor will have.

Windows do have a scaling factor you can apply to your monitor, but this just make it behave like a lower res one, so it is a waste of money, and not all programs work correctly with the scaling (CC3+ works mostly, but there are some issues in some dialogs).

Of course though, all of these considerations are mostly related to the internal monitor of the laptop, since that can't be changed once the machine has been bought.

Having multiple external monitors are always a good thing though. On my fixed setup, I have 4 (+1 (+1)), it really helps productivity.

I do mostly agree with JulianDracos and Kertis Henderson here. 1TB drive/16GB ram is fine, and as Julian says, a fast processor is better than a slow one with many cores, although a certain amount of cores is highly useful (I recommend 6 or more, but most CPU's will fulfill that today)

As for the screen, I fully agree with Kertis, don't get a 4K one. I used to have one on my old Work laptop, and it was a pain for most things. I prefer to go a bit higher than a full HD (1080p) screen though, I find a 1440p one much better. But there are two factors here, first of all, your eyesight, 1440p naturally makes things smaller (and buying a 1440p just to increase the scale factor in Windows is a waste), so make sure you're comfortable with the size, otherwise do go for that 1080p one. And of course, a higher resolution screen do mean CC3+ is a bit harder to run, so it should only go along with a somewhat good CPU, if you go budget on the CPU then do not get a 1440p screen.

My own laptop is a Lenovo Legion Pro 5 (1TB/16GB/i7-13000hx/RTX3070/2560x1600), a machine I find well suited to most task and pretty good value for money.

The only way is really to just load them up in the house style editor [HOUSEOPT] and look at them one by one.

To quickly look through them without clicking yourself to death, take advantage of the fact that Windows GUI components are keyboard friendly. Simply use the top dropdown and click on the very first style in the list to select it and collapse the list, then as long as you don't click any other controls, it will be the active control, and you can go through the styles using the arrow keys.

The best option is to keep the template lines in a clean file.

If you copy them over to another (temporary) map, you can just go wild in that one, deleting all the fill styles. You'd have to do it manually, but at least you don't need to consider which to keep and which to delete, just do them all. Then you can copy the lines from this clean file afterwards.

(You may want to save that temporary map every now and then, mass deleting fill styles sometimes causes CC3+ to crash)