What is the minimum shipment for sea freight from China to Thailand?

Yes, but it is small. On CIMPEX's consolidated China–Thailand lines the minimum is 0.5 CBM for furniture and general goods (anything smaller is billed as 0.5 CBM) and 200 kg for weight-based heavy cargo. That means even a single armchair, one bathroom's worth of fixtures, or a sample order can ship on the same direct line as full projects — you do not need to wait to fill a container. Full containers of 20 CBM and above are quoted separately at better rates.