It essentially helps 0-conf transactions by protecting against double spends, and will likely help block propagation and scaling. I think it also might prevent some other problems.
If a transaction meets Avalanche consensus we can feel safer accepting the transaction knowing there is no double spend, even if it still has zero confirmations on the blockchain.
The BCH devs are looking to see if Avalanche consensus can be used as a preconsensus for transactions. It just manages the mempool for miners to process transactions from.
Not by definition but I suspect it quickly degenerates into PoS. How else can you trust the Avalanche data for anything? Not surprisingly, AVA coin is PoS
You can base the weight of votes on POW. Yes AVA coin is PoS. Whatever this you are saying is speculation. I think Avalanche is awesome but I'll leave if BCH becomes PoS.
I don't think Avalnche becomes any more complicated if it relies on PoW, or PoS. It is it's own consensus form, and is independant of the PoW done by miners.