[MihaiAlisie]

First of all thanks for the encouraging words!

> If a user is to run a "node" on their PC, how will the network react if a friend/follower is offline when data is requested from them.

There are some things currently in development such as IPFS clusters that can tackle this issue. There's also the IPFS filecoin token (not yet live) which would provide an incentive for people to keep the hash "alive". This is similar to how Ethereum's Swarm will work.

In the meantime the gateways mentioned in a comment bellow would act as a sort of "seed" even if the OP goes offline.

> will a node be runnable on a home server system, allowing for higher-availability and easier backups of personal data?

I don't see why not. Remains to be tested though :)