About the ordered quantity
Generally speaking, the standard of hot dishes for one person is appropriate, and more is not enough (so ordering food generally does not cause waste). Cold dishes depend on the situation. Generally, even numbers such as 2, 4 and 8 dishes are appropriate, generally no more than 8 dishes.
Order a double instead of a single.
For example, if there are eight people dining, they usually order eight hot dishes. If 9 people dine, order 10 hot dishes. If it is not enough, two more dishes are usually added. But if you think adding one dish is enough, you might as well add one dish when the minority is subordinate to the majority. Ordering a double is not only because it means "yes-man", but also pays attention to good luck when eating.