Slow model....do I need to upgrade my PC?

Sorry to break in but if it's slowness of Sketchup, there's not much you can do about it other than using a lot of proxies and keep the models (geometry) small.

For Enscape a nice GPU helps big time but for Sketchup itself a fast GPU or CPU doesn't do that much. If you've complex geometry you need in Sketchup you should really try to use all complex things as proxies instead of just directly importing them into your model. Else you will drive yourself crazy by the slowness of the viewport.

For example, a lot of the models you find on 3D Warehouse are converted models from other file formats. While they look nice they often have way to much detail to use directly in Sketchup. Therefor it's smart if you convert those models you want into Enscape proxies so you still can work fast in Sketchup and the models show in all glory if you open Enscape.

Basically it's the same for all 3D programs but especially Sketchup is not really well fitted for people to import all furniture, garden plants etc inside Sketchup with their full geometry. There are also some general tips to speed up the viewport/modeling process like hide unused items (or those outside the group you work in) don't enable 'show hidden geometry/objects' and in the past having the outliner panel open was also a real slowdown of Sketchup (think that's better now).

TL:DR;
In case you've an building, just have that building as full geometry and everything inside and outside as proxies. If you want to stay flexible all separate proxies but if you don't need to move those around you can select all and create a proxy out of everything besides the building. What I also often do is having two files, one with all 'extra's' and one with just the building. That's where I work with and the other SU file is for render. F.e you could also have your model as a linked model in the more detailed file so it will always reflect the changes. Mainly you've to work a bit smart with SU if you don't want to get too frustrated

Tracyheywood I think this Sketchup page is pretty ok if it's about modeling smart, it also includes a long (older) video I didn't check but I guess it should treat some basics well. It's old but Sketchup didn't really get any faster past 10 years Without being too technical, all new CPU's have like multiple cores and such, great if you render things but Sketchup will only use 1 core/2 threads maximum I think. Mainly because some tasks can't be divided into sub tasks easily and especially if you use some plugins on complex geometry that can be terribly slow even if you have the fastest CPU available.

This is the page I found with some Sketchup basics: Improving Performance | SketchUp Help

The proxies are used in many pieces of software. It's the same as if you pick a asset from the Enscape library you see a simplified shape but once you turn on Enscape you see all it's geometry (from that moment your GPU gets important). Because those shapes are so simple they don't use up a lot of processor power you need to work fast in the viewport.

In Enscape it's really friendly to create your own proxies from complex models compared to some other tools I use. Basically while having your 'complex' model open which you want to turn into an proxy/asset for Enscape you open the Asset library, click the tab 'custom assets', click plus sign and you get a step-by-step to concert the model. Just be sure you keep the original model at the same place so it's easier to change things later and Enscape always keeps the link to the original.

A good way for example is creating a folder in documents where you have the original SU files you for example downloaded from the warehouse and turn into proxies. Maybe even with subfolders for categories, just what you think is handy. Also try to be smart with the naming of models, a lot of 3D warehouse things are called Untitled.skp and that doesn't really help if you want to find something later on.

After playing a bit with proxies you'll notice how useful it is. The only thing to consider is that if you create a model for a client who also wants the model as a file, to make sure the client understands he doesn't get a SU file with all geometry. Rare case maybe since most won't give clients the skp I think.

Anyway, don't worry too much about hardware in SU. I used to have a 1070 (well, 2) but got a 2080Ti gifted from an online race friend from Finland. And yes, in Enscape and other render tools that makes a huge difference. So I gifted one of my 1070's to another Dutch guy and already curious what the Finish guy will do with his 3090 if the nVidia 40xx comes out

Since you are a starter, you most of the time also take longer for projects. Maybe you can make a deal with a client that instead of paying a normal bill they can buy you for example a nice graphics card. Not sure if that's legal in your country but here some clients like that idea since they can deduct those costs from tax/profit so while you end up with a nice GPU they might be paying even less netto. I've zero budget at the moment but some of my former clients helped me out with my change from 2D to 3D designs buying some hardware.

Good luck!