Should I buy mid-range DDR5 now and upgrade later?

Yes. High-end DDR5 kits are overpriced for marginal gains today—real-world performance difference is often 1–3% while costing 2x or more. Mid-range kits (like DDR5-6000 CL30) work reliably out of the box, and faster DDR5 will be cheaper and more stable in a few years. Put the extra money into a better CPU or GPU instead.