With the above strategy, you should be able to preserve your data for as long as you can actively curate it. In case you want more robustness against accidents or the risk that 2 copies get corrupted under 5 years, then you can make more copies, preferably as LTO cartridges, but it can be other hard drives.

For more information on how to cold store LTO drives, read pp32-33 "Caring for Cartridges" instruction of this user manual. For HP LTO6 drives, Matthew Millman made an open-source commandline tool to do advanced LTO manipulations on Windows: ltfscmd.

In case you cannot afford a LTO drive, you can replace these by external hard drives, as they are less expensive to start with, but then your curation strategy should be done more frequently (ie, every 2-3 years a small checkup, and every 5 years, a big checkup).