1. Yes, this is the typical museum method for archival framing, assuming you just attach the print at two places at the top (three for large prints). The print will expand and contract at different rates than the mount board or mat board with temperature changes. If you use a solid piece of tape on the top or other edges then buckling will likely occur in a short amount of time.
Yes, it might curl a little, especially if you are in a high humidity area such as coastal region. If the humidity is reasonable and the paper is a decent thickness, it may not curl at all. I have lots of prints hung like this that have not curled. Fine art collectors realize this is archival printing because it allows the print to be easily removed from the frame and placed in a new frame. Of course if you are in an area with serious humidity problems then the wood in the frame may warp.
2. You can use
Frame Sealing Tape to seal between the mountboard on the back and the edge of the frame. This can help keep out dust and reduce moisture.
3. This is mostly personal preference but typically I would use at least 2 inch borders for 18x14. As long as the frame is larger than the paper you will not need to trim it.
I am the owner of Frame Destination where some other links were posted and we have
additional picture framing info.