The 9900k is too expensive, for what you can get from AMD.
Now for a first build, I would get something like a 3700X for a good balance of gaming and workflow.
Get 16 GB of ram, Phanteks makes bad ass cases, For cooling I would go with a dark rock, or an AIO like the NZXT Kraken.
Get a good power supply from the Tier list (basically buy something gold from a good brand)
For GPUs, I would wait and see, how aftermarket 5700 and 5700 XTs are, before jumping on super
You can DM Me, if you have any questions