It sounds like you are Ok with connecting your external hard drive to initiate a backup. When my daughter went to University I bought her an Apple AirPort Extreme and a USB Hard Disk, and set her up with Time Machine, so that her Laptop was backed up every hour when she was in her room and her laptop was connected to Power. Time Machine can be a life saver for students when you accidentally overwrite or delete your essay and you can use time machine to roll back to the last backup version.
Unfortunately Apple have recently discontinued the Airport range. I don't have one, but I gather the Synology, range of NAS drives can be connected to a WiFi router and achieve the same result as an Airport Time Capsule, the model DS115j appears to be designed for home users in mind. However just getting a USB 3 external drive is a much cheaper option, provided you are organised enough to remember to connect it on a regular basis.
Online backups are great as a secondary backup system, as it gives you full protection against fire and theft of your physical devices - Laptop and Backup device. Also online backup systems give you the benefit of automatic backup without having to remember to connect your external hard disk. I am not sure I would recommend them as a primary backup solution though, if you have a total hardware failure and you lose all, or most of your data, it can take a long time to restore. Many services do offer to send a copy of your data on a drive at an additional cost, but not as cheap or convenient as having your own local backup solution.
Then use CarbonCopyCloner (or SuperDuper) to create and maintain a CLONED and BOOTABLE backup of your internal drive on the external SSD.
Now -- if a disaster happens, such as the MPB gets stolen or damaged -- you still have an IMMEDIATELY-ACCESSIBLE fully bootable copy of the internal drive that you can connect to another Mac and KEEP RIGHT ON WORKING. It will look just as your internal drive "looked".
Or -- use the backup to restore to a replacement MacBook.
If you get into an "I can't boot!" situation, nothing beats having a bootable cloned backup.