Ignore what Time Capsule says and look at the two computers you're using to determine how much disk space is being used. Increase that by 50%, get an ext FWHD, partition it to hold each HDs data + 50%, and use something like Carbon Copy Cloner or SuperDuper! to put bootable backups/clones of each machine onto it.
Without a doubt it is NOT Dropbox. Take a look at the free software by Google -> Picasa. Any platform, and massive volume of storage via google 25gb, which is all online and you can easily expand on. Syncs very quickly and does face recognition so you can group images by whos in them. Has a great timeline function. Effortless.
I had one of my cd's that I burnt that wasn't readable after two years. I was annoyed. I had paid to acquire the data.
I did the old internet search on "dvd lifespan last". The lifespan varied a lot. The quality of the media is important. Gold colored then silver colored are best. All agreed on this. Several private bloggers gave 50 to 300 years. The US National Archives gave a lifespan of 2 to 5 years to other government agencies. This is the years for which you can be 100% assured that you will be able to read every dvd you write.
6. How long can I expect my recorded CDs/DVDs to last?
CD/DVD experiential life expectancy is 2 to 5 years even though published life expectancies are often cited as 10 years, 25 years, or longer.
It is wise to research this field carefully. My early CDs were useless after 5 years but I have yet to discover any difficulties with my Verbatim DVD +R.
The 2007 NIST/Library of Congress Optical Disc Longevity Study implies about a 50 year life for DVD R:
Here are a few of my random thoughts:
1 - Safest, but not practical, media - punched lead (Pb) tape
2 - Do automated verification read after writing
3 - Keep all critical data on more than one type of media located in more than one place
4 - Infrequently used backup hard disks can be expected to have a much longer life than frequently used disks
5 - In general lower density hard disks are more reliable
6 - In general server grade disks are more reliable than desktop disks
7 - 5 inch desktop disks are more reliable than 3 inch laptop disks
8 - 10 year old disks less than 60 GB with proper MTBF specifications may outlast most more recent disks
9 - Compression or any type of security coding will reduce the likelihood of recovery