Really cold in Scotland at this time of year? Need heavy sweaters, coats? All I read is about the need for constant rain gear? Is that overstated or real?
Haven't been in Scotland in Sept. or Oct., but was there last month (August) and also in April, and got rain often. Having a waterproof raincoat with a hood is essential. Unless you're at the top of a peak, I don't believe it ever gets extremely cold (like the minus 40's the Colorado mountains receive in the winter), but it can be cool, so layering with a sweater or other warm items wouldn't hurt. The wind blows on occasion, as well. There are more than a few sheep over there, by the way, so you can also pick up a great sweater or two once you arrive!
No, you need rain gear. As they say, there is no bad weather just inappropriate clothing. How great it will be if you don't need it, but you will get very wet if the normal weather prevails.
And I have traveled in September. I recommend layers. You can always buy these items if you want to risk it. There are great sweaters and great rain gear to purchase all over Scotland. :)