Buy the matched kit now.

Yes, buy the 2x16GB kit today instead of piecing it together later. Dual-channel memory works best when sticks are identical—same timings, same voltage, same silicon batch. Two single sticks bought at different times might work fine, but they might not. You risk instability, lower performance, or having to manually tweak settings. The price difference is usually small, and the headache isn’t worth it. Future you will thank you for not gambling with RAM.