I don't think you can tune the delay to achieve two goals: make it impossible for botnet to exchange information (~4*transmit time) and make it possible for slow nodes to successfully transmit a block (sometimes 200ms to geographically near location is not that unusual).
Its something we're thinking about, we might require clients with very slow connections (ie Africa) to transmit more confirmations at a time. Since most clients will be connected through their ISP since they will be sharing IP ranges I think most confirms will be rather fast.... testing will tell us.
Also, how much disk space do you expect to use? I would not give any coin more than 20GB of my precious HDD. Even bitcoin.
The blockchain will be as big as the block chain gets, there isn't much we can do about that... although with an wallet like electrum you wouldn't have to download it all. I wouldn't be too concerned about the size just yet, BTC is still only around 14gb. You will be required to use a 8Gb USB stick for farming however.