As an alternative to the 3700X, it might also be worth considering AMD's new 5600X, which should be available for purchase in a few days. The 5600X should cost about the same as the 3700X, but has 6 faster cores based on their new, improved Zen3 architecture, compared the 8 Zen2 cores on the 3700X. While independent reviews are not out quite yet, it looks like the 5600X will likely offer over 20% more CPU performance per core. In some heavily-multithread tasks that can fully-utilize all cores, the 3700X might manage to be slightly faster, but that doesn't apply to the vast majority of applications and games, where the 5600X will almost certainly be the faster processor due to its notably higher per-core performance.
Probably worth asking, do you have a screen for the computer already, or are you looking to get one? The resolution of the monitor could largely influence how much you want to spend on a graphics card. At 1080p, something like an RTX 3070 might arguably be considered a bit overkill for today's games, but at higher resolutions like 1440p or 4K you might see more benefit from a graphics card in that performance range.