Sounds like you did a great job. Here are my 2 tips, based on my experience:
- For postage, if your location has a self-service kiosk, you can use the kiosk to easily print ready postage for trades. I select 'print postage' and you can pre-print with the extra postage that the non-machinable charge costs. This comes to about 78c - 1.00 total each (depending on what oz. you choose), and they print on individual stickers. I print a variety ahead of time and just ballpark the weight on each (i.e. print a bunch of 1oz. 2oz. 3oz. to keep available) and I've never had an issue.
- You can avoid buying packing material by getting the free letter mailers at the post office (the kind priority mail uses). The width of these you'll find is exactly the right width to fit a card binder page, so all you do is make one quick long cut to get the envelope height and you've got a nice cardboard protection.