As you can remove all panels, including the one on the top, assembling your parts within the case should be no issue at all. All the components are essentially mounted on the exterior planes of the case, facing inward. As the 90° angle for the GPU to PCIe slot is intact, you don't even need to worry about a riser cable. On the left wall of the case, there is the motherboard area as well as the PSU bay. On the other side, the space is utilized for cooling in the form of three 120 or two 140 mm fans, or an AIO of up to 360 mm in size. In the front, you may install three additional 120 mm fans. In the Corsair 2000D Airflow, these are optional, but you can opt for the 2000D RGB Airflow which ships with three iCUE capable fans.
At the solid top panel, there are two Velcro strips, so that you may easily route power out the back of the chassis. The SFX PSU bay is held in by screws and may be removed if you feel the need to assemble things outside the chassis. It is spacious enough to accommodate SFX-L variants as well.
Looking at the floor, any excess wiring for the front I/O can nicely be tucked away here, out of the way of all the components. There are three slots for modern GPUs including any GeForce RTX 4090 as long as it is a true 3-slot card. Perpendicular to that, there is the motherboard area, where you are meant to install the board with the backplate facing downward, so that the PCIe slot lines up with the expansion slots. At the top, on the PSU bay, there is a singular SSD mounting plate. If you look closely, there is another mounting position for a second placement opportunity. In fact, there is a third, right next to the one on the PSU frame, but Corsair doesn't actually include the plate for this one. Considering it sells for just $3.99 on their site, it makes no sense to not simply include it in the case and give customers all the possible storage vs. just advertising a theoretical possibility. Lastly, there are two further sets of holes in the ceiling as that is where you would find the PCBs for the ARGB variant installed.
In the rear, there is the big, somewhat basic vent which is meant to provide fresh air access to your GPU. Alternatively, if you are using a slim enough pixel pusher, you could also install two fans of 120 mm size.
All the wiring within the Corsair 2000D Airflow are of the standard, black variety. Even the USB 3.0 connector itself is black, which tends to be blue for a lot of other cases out there. While many brands have started moving towards a unified motherboard header connector, Corsair is still sticking with the separated one to ensure 100% motherboard compatibility.