Personally, I think you need a complete overhaul. If you upgrade your graphics card, your CPU will quickly bottleneck it. The terrain lod setting will play a large role in getting clear ground textures, but also one of the larger CPU impacts when you increase it. Being cpu bound not only means lower frame rates, but also worse stuttering. I currently have an i5-8400 and it just barely keeps up in that department.
Your ram being 12 GB likely means it’s mismatched sticks, such as a 4 and 8 GB stick. Memory works best when using a matched kit, so you are likely leaving a lot of performance on the table there. This actually sounds like a prebuilt system because they are known for such shenanigans, which also means a lack of optimizations in general.
I would say if you don’t care much about the graphics at all, the CPU I have would do ok, but also means upgrading the motherboard. Not sure if your RAM is ddr4, but I would upgrade that to standard 16 GB kit minimum and something faster. At that point, a 1080ti card could be doable (I started with a 3 GB 1060), but not all that great. You don’t need a screaming system to run this at low settings, but a bargain basement system isn’t going to cut it. The 1080ti will likely being obsolete before long too.
If you think you’ll ever start adding mods, well you can throw all that advice out the window. I’m only considering you playing only the base sim with no add-ons.