10 nodes is as simple as setting up 10 computers to be nodes, not sure if you need individual public IPs for them, etc. Currently there is an estimated 6825 updated nodes according to bitnodes (https://getaddr.bitnodes.io/).

The difficulty is based on keeping the time to solve a block at 10 minutes, so not sure about your attack vector.

Assuming you are attacking the last block before difficulty change...If you dropped your hash 1kh/s and still somehow manage to solve the block at your first attempt, then the difficulty would increase not decrease, as it would need to average out to take 10 minutes, making your now isolated blockchain behind the distributed (legitimate) blockchain.

Assuming your attack is attacking the block to get difficulty to change from anywhere else between the creation of the new difficulty to before the last block before the change: the estimated time for solving a block with 1kh/s is 1723055322786 days, so this isn't a practical attack method (calculated on https://tradeblock.com/mining/).