Will foresters clear stone and iron

Yes, multiple trading posts means more trade boats. PeebleTheory confirmed this in this video. At ~4:30 a second trade boat comes by while he is already trading with one trade boat and it goes to his second trading post.

A few facts to consider:

• Students graduate at age 16 if they live next to the school. If they have to walk (back and forth) to the school, that walking time does not count toward education progress. This is why players are reporting 20 year old students.

• Education gives the worker a ~50% productivity increase. However, education does not make a worker walk faster. This means that hunters, gatherers, foresters, laborers, vendors and tradesmen do not benefit much from education. Fishermen, miners, quarrymen, firewood cutter, blacksmith and tailor all benefit from education.

• Having students locked up in school delays the creation of couples. This could tip a city that's on the edge into stagnation. If you have fewer than 10 children, you should probably be focused more on making more children, rather than education.

• Education also reduces random accident death, so you'll want it eventually.

So, putting it all together, I'd build a school when all of these criteria are met:

• There are more than 10 children.
• There are more than 8 workers in non-walking jobs.
• There are no more pressing needs (food/firewood).
• There are at least 4 spare laborers (+1 to be a teacher) to handle the gap created by the first wave of students.