1. Yes. Not everyone in game checks the forums here, so you should still open a shop with all the items you are selling. Also, be sure to check back and see if people respond to your thread.
2. The housing board allows you to search items that are up for sale in people's houses.
3. When someone puts "note me," it means they may want to negotiate a price and/or trade for an item you have for sale. If you do not open a shop, then yes, people will exchange items with you in a trade. Items are usually just sold in a shop, unless it's an item that people are bidding on, in which case, you do not put that item in your shop, and when the bidding is over you trade that item with the person who had the highest bid.
4. The mailbox for mailing items is only good for when people don't want to meet in game to trade with each other. It's useful for when, say, you're trying to sell an item to someone who lives in a different timezone, so you're not online at the same time. In that case, you would mail that item, and click the little box that says "request gold" and enter the amount you want to request. The person cannot get the item you mailed without paying the requested gold amount.
Let me know if you have any more questions~ And good luck with selling!
Thank you sooooooo much! These answers help majorly
I do have one more question.
What happens to your shop after you log out?