Get the dual-channel kit now.

Yes, buy the 2x8GB 3200MHz kit now.

Ryzen is sensitive to memory speed and dual-channel configuration. Running one stick in single-channel mode will cost you 10-20% gaming performance — sometimes more. The Ryzen 3 3100 is already a budget chip; you don’t want to starve it further.

The hassle argument matters, too. Finding the exact same stick later is unreliable. Mixing sticks can cause instability or default to lower speeds. And you’ll be stuck at 8GB in the meantime — which is tight for modern games.

Spend the extra $30–40 now. Future You will appreciate not having to open the case again.