Before buying a media card (mSD-HC), consider this:
Applications and their saved data don't save to a media card.
Photos, Videos, music, downloaded files and documents you edit as well as attached e-mailed files do.
You have first to identify the space "eaters" you have on your device. (some What'sApp fun video files can be really large and can be deleted without any regret to liberate many GB of storage space!)
Then, know that your device is safe from spying eyes even when lost because it does a security wipe if ever found and password faulty.
A media card is by default not encrypted. If you want to save sensitive data on it, you should encrypt it. However, the encrypted card is then tied to the device and can't be read in an external card reader for a faster data transfer to computer. That's why I don't encrypt mine.
Many things to consider. Maybe you just have to "declutter" by saving some data using Link to your computer then simply delete from phone to create a little bit of space.
Workhorse: BlackBerry|Q10, SQN100-3, OS 10.2.1.2941; Power Workhorse: BlackBerry|Passport, SQW100-1, OS 10.3.0.675; Germany.