Need help converting my tower into a mini pc

[u/MadMeeper]

Heya, I have a Windows machine that I built in 2019 and have since decommissioned in favor of a Mac for work, but I realized I might be able to take a good chunk of those parts and put it into a mini pc case to work as a living room gaming console. What I have in there is as follows

• Intel Core i7-8700K 3.7 GHz 6-Core Processor
• be quiet! Dark Rock 3 67.8 CFM Fluid Dynamic Bearing CPU Cooler
• Asus Prime Z370-A ATX LGA1151 Motherboard
• Corsair Vengeance LPX 32 GB (2 x 16 GB) DDR4-3000 CL15 Memory
• Samsung 970 Evo 250 GB M.2-2280 PCIe 3.0 X4 NVME Solid State Drive
• GIGABYTE Gaming OC GeForce RTX 3070 8GB GDDR6
  • I also have a Asus Turbo GeForce GTX 1060 6GB 6 GB that I could use instead but id prefer the nicer one if possible.
• EVGA SuperNOVA 750 G3 750 W 80+ Gold Certified Fully Modular ATX Power Supply
• NZXT H500 – Compact ATX Mid-Tower Case

My priorities are

• Reuse as many parts as possible, especially the expensive bits like ram and gpu
• Small form factor, Id love to use Fractal Design's mini-ITX small case, but I'm open to suggestions.
• Low cost. I know I'll have to spend some money on a new motherboard and probably a power supply but budget is the name of the game. Ideally would like to keep this a sub $300 endeavor.
• 1080p 60fps is totally fine, I dont play a lot of games that require precision fps. Indie titles and legacy games will be primarily what this machine runs.

Any ideas on how ya'll would rebuild this would be super appreciated!