1. Your routing to DPS looks good.
2. Don't splurge on J DPS-SYD. That's a waste. It's a 5.5 hour flight, likely a redeye, and unless you hit jackpot on GA you won't get lie flat. And VA J is domestic FC.
3. CI > CZ > MU. Try to get back on China Airlines - you would have to search separately for this, MEL-TPE (redeye on angeled lie flat a330) and then a FANTASTIC 777 to LAX. Check SFO as a destination, too. China Southern is better than MU so if you can go through CAN, try that instead.
4. Don't waste cash on mainland china premium economy. And don't expect any other real premium economy for < 2k. That said, Air New Zealand sometimes runs PE sales and you may get lucky.
5. No upgrades on Virgin Australia. Welcome to OZ!