I was willing to setup a private ethereum network with low difficulty. I can fix the difficulty of each block to 1 (or constant) to avoid problem of very high difficulty with increase in no of blocks.
But this has a downside of decreased block time and hence running out of disk space sooner.
Is there any way geth source code could be modified to remove miners reward and hence coinbase transactions? So a block is added to chain when there is some real transaction. This will save disk space to great extent and we can enjoy constant difficulty.