Besides emergency fund, how much "spare cash" should I hold?

Great, simple question :)
Since you've already prepared an Emergency Fund, how much 'spare cash' depends on you.

As mentioned earlier, an additional 2-3 months of salary, while taking into account factors such as lifestyle & commitments are great rules of thumb as guidance.

For some, they'd wanna create a liquid cash budget for house renovation or car / house purchase downpayment, while others, in case they want to go for a 3-6months travelling holiday, without touching their endowments and emergency funds. Others just want to see $250,000 or more cash in their bank accounts.

If you prefer to grow your spare cash, then it all depends on your preference, ie either a savings account with higher interest, unit trust, ETFs etc.

At the end of the day, the question still boils down to how amazing do you want your financial castle to look like? :)

Depends on your personal circumstances etc single vs family commitments, low vs high flyer lifestyle

6 months would be a recommendation.

I would recommend 3 months of your salary as spare cash on top of your emergency fund.

In the event, if you fire your boss or your boss fire you, you have 3 months while you find another job.