You can get remote access to the TC via BTMM and iCloud.
See the info prepared by Tesserax.
https://discussions.apple.com/docs/DOC-3413
Apple explicitly say not to do TM backup remotely.. remember your connection over internet is always reduced to the slowest link.. in this case either upload at your end or upload at the friends' end.
Using the TC as external hard disk is often asked.. and alot of us who see the problems that result say.. don't do it. The TC is designed for TM backups.. not as a data store or NAS.. it has several issues.
1. Storing TM backups and data does have issues.
See Q3 here. http://pondini.org/TM/Time_Capsule.html
2. The TC has no backup abiity.. it is not designed to function as a NAS.. all of which have backup built into the device.. proper automatic incremental backup. The TC cannot be backed up by TM as it is a network drive.. to back it up you will need to buy a third party product.. eg CCC and backup to where??
Once you move files off the MBA and onto the TC those files can be lost or corrupted.. so don't just think backup doesn't matter. And backup over wireless is extremely slow if you do decide to use CCC etc.
3. Some software can easily corrupt itself.. iphoto for instance and especially over wireless will corrupt a file and cause the whole library to be corrupt.. this is the reason to not do it over internet where file corruption becomes even more of an issue.
Get a fast external disk using the thunderbolt usb3 or fw800.. all much better than usb2 which is the cheapest but last in the list. 2.5" drives are small and light.. or a computer with a larger SSD or proper secondary drive.
