Officially both chains will be competing under Nakamoto Consensus. This means that the chain with the biggest collective proof of work is the "true" chain.
Isn't Nakamoto Consensus that the protocol-abiding chain with the most PoW is followed? Therefore, if there is a chain with more PoW that doesn't follow the protocol, that has no bearing on the consensus chain. It's the economic nodes that determine the protocol.
Under your initial argument, BCH would currently not be following Nakamoto Consensus because BTC has a higher hashrate.
BCHSV miners plan to attack BCH by mining empty blocks
This would be interesting to witness. Are they also planning to combine this with a 51% attack to orphan any block that has transactions?
Yes that is correct. I think that when they say that they want to compete under Nakamoto consensus that they say they want to vote on the fork using the Hashrate. The "true" chain is the one that has more POW. By that criterium it is very clear that BTC is the true bitcoin and not BCH since it has much more POW, but all of this is of course convention.
I dont know this, but when they have more than 51% it would be stupid not to. The already made an attack on the testnet and there were only empty blocks for more than 6 hours. Of course testnet hashrate is low, but this suggest that they also did a 51% attack.
In any case, they may disrupt the BCH chain, but in the long run this (probably) wont work. It could howoever disrupt BCH during the fork so much that the value of BCH drops and has big trouble recovering from that.