I would avoid the Aurora R7 and any Alienware system in general.
The R7 has one m.2 slot and its compatibility with the m.2 ssds on the market is quite low. You will have it try different ones out.
The hard drive can be replaced by a larger one with no problems.
To go further with why I would advise you to steer clear:
-Very bad memory compatibility at high speeds/low timings. The motherboard will only boot up with 2933mhz max.
-Terrible case layout. The PSU is right up next to the CPU and the GPU is directly below the PSU creating a small hotbox and blocking the airflow from your front intake fan to the top exhaust radiator.
-The aio uses only a 120mm radiator which is really too small for the CPUs they're putting in the Aurora R7. They make up for the small radiator by using a jet turbine Nidec 120x35mm 4500rpm fan that regularly reaches 50dba based on your load.
-The motherboard is gimped. They bifurcated the PCIe slots to x8 only. Sure you can do SLI/NVLink x8/x8, but if you're sticking to one card you're only getting x8 no matter what.
-The alienware overclocking controls have no advanced options. You can only change frequency, voltage, and voltage offset. The same story applies if you enter the BIOS. Its barebones.
-Finally, Dell Support Assist is built into the motherboard and you can't disable it! If you want to change your CPU fan to something quieter or better, you will have a forced fan test at boot that lasts for about a minute. You cannot skip it, it is unavoidable.
-Bloatware! I'm not sure if is the case with all of them, but I took large latency hits testing with Latencymon.
The Aurora series from alienware is not a good deal. They cut corners and use cheap parts. I got suckered into it with my first "premium" PC and I regret it. I will always recommend building your own system. You'll get exactly what you want