Backups are EXTREMELY important. Always remember that a backup drive is just that and you should let an automated process manage your backups. When the drive is full, remove some of the older backups to make room. If your backup drive fails, you still have the originals. Replace the failed drive and resume backups. If your main drive fails, all of your data is stored on the backup drive. Replace the main drive and operating system, access the backup drive, and replace your data files.
Nothing is as precious as the air we breathe. Computers like to breathe also. Don’t block off the case airflow as you can create overheating issues. Most cases have side vents and you want to make sure to leave at least an inch of space on the sides. Watch the backside too .. the big exhaust fan is there to get rid of the heat; you don’t want to block that one either.
You don’t always have to replace an older machine. Sometimes you have to weigh the pros and cons of replacement vs repair. Most machines can get additional speed simply by upgrade some of the internal components. Adding memory goes a long way. The difference between a mechanical drive and a solid state drive is amazing.