I have a lot of data to back up and I'm concerned that backups will take a long time. Will they?

The speed of the backup depends a lot on the upload speed of your Internet connection. For most Internet connections, the upload speed is often something like 1/10th of the download speed. So, backing up for the first time may very well take a long time. The backup software is incremental, however, so after the first backup, only new changes will be sent over the Internet connection. Therefore, after the first backup, subsequent backups will be a lot faster.