Imperial Japan is useful for helping to finish off the British - not least by taking away their tin and rubber production in Malaya and adding to the chaos and unrest in India.I think Germany never should have got involved with Japan. They were too far away to assist each other in any significant capacity.
Also, Germany had plenty of business interests in China. They could have kept up the civilian business contracts with China while not opening picking a side in the China-Japan war. (Covert weapons shipments could continue???)
that would draw US attention away from Nazi Germany and after OP Barbarossa, Japan would still attack Pearl Harbor. They only needed assurances that the USSR wasn't going to crush them in Manchuria.
A Japan-first policy would give Germany a better chance at winning a Limited Victory.
The problem is Germany needs Imperial Japan in as soon as possible, and ideally without bringing the United States fully in as well.
And I think the Imperial Japanese might feel constrained in their ability to act by wanting their naval building program as far forward as possible 'just in case' and as much of French Indo-China occupied (and with at the very least airbases established there) as possible.