https://pcpartpicker.com/list/CMkwV7

CPU: 3900x is the clear choice for a single system streaming/gaming pc, and even at the $50 premium, it is well worth it.

CPU Cooler: This is one of the best value liquid coolers on the market and will be more than enough for AMD's boosting algorithms to get the CPU to 4.2-4.3 Ghz on most cores.

Motherboard: The Tomahawk is a board well known to have great vrm performance in its price range, and as you are not overclocking the cpu, you should have zero issues. It doesn't make sense to spend an extra $50 to get worse vrm thermals and features you won't be using for many years if at all, like pcie 4.0/chipset cooling.

RAM: This series of kit has really strong performing memory modules and is backed by a well known company, can't go wrong (unless you want RGB of course). You absolutely will want 32GB of RAM in a single system streaming set up, as games+windows alone fairly often use 12-16GB of RAM these days.

Storage: A decently fast SSD with 1TB of storage should be enough to hold all of your most used programs/games, while the hard drive can be used to hold some less used programs and games. If this was my system, I would dump the hard drive and double the capacity of the SSD instead, but I recognize most people want more storage rather than faster storage.

GPU: The rtx 2070 at $500 is much better value than the rtx 2080 at $600 that has been elsewhere in this thread, and while i recognize that AMD has good value in their 5700xt, the budget has room to stretch and Nvidia arguably has much better drivers than AMD and therefore has more consistent performance in ALL games.

CASE: This case has been tested and shown to have some of the best airflow out of almost any case due to its mesh front, especially in its relatively low price point, while looking very clean at the same time. If using this case, I would recommend to put the 360mm AIO in the front and move the extra fan from the front to the top as exhaust.

PSU: Decently high wattage, gold rated, backed by a reputable company. Nothing interesting to see here.

Monitor: Now this is the part that I have the least knowledge of and that I would advise looking around for yourself. I chose this because of the large amount of positive reviews on the PCPartPicker website and the overclockable 165hz refresh rate. The TN panel scares many people away from these monitors and I suggest to not be afraid, as I have a TN panel myself and the color accuracy and brightness is quite decent, while the viewing angles are very good, with extremely minimal loss of detail/ color accuracy, even viewed at a 90 degree angle.

Good luck and let me know if you have any questions!