Nice topic, I also have to decide tomorrow regarding the terrace dimensions.
In the building application, 7x3.5m was specified, but I am strongly leaning towards definitely larger (deeper) after the space in the garden there was cleared of greenery.
I would make a terrace at least 4m deep, if space allows, 4.5m deep.
Because as previously mentioned, it quickly becomes tight if the chairs should not be placed directly at the edge, there is a wider table in between, and the foot traffic should not interfere with each other.