I used to take bus from JB Sentral (building that's linked to the JB CIQ building) to KSL, until those buses from Jalan Wong Ah Fook moved there too. Just find it messier. That's when I started using GrabCar, having before that only used GrabTaxi in Melaka.
But I normally Grab from Komtar JBCC (mall linked/next to City Square) instead, as I find there are less human and vehicular traffic - easier to spot each other.
Over at KSL (as with any other destination), choose a spot to alight that's not near to a taxi stand, like the Coffee Bean entrance that's also the hotel entrance side. The other entrance/exit is more commonly known as the KFC one, which is Lower Ground (LG or basement) of the mall, same level as Tesco supermarket.
Going back from KSL on a Monday night will be more challenging as the road with the pasar malam has traffic restriction, one side is closed. Over at the KFC side, there's a taxi stand (too many carrots for those drivers to chop on a Monday night), and the queue for the bus (move here only on pasar malam nights) can get quite crazy. I'd advise crossing over to the hotels opposite to GrabCar instead.
You can go shopping earlier in the day, then leave for the pasar malam about 5pm, check out Cedar Point, then head back home. Otherwise, take your own sweet time by staying a night in KSL Hotel. Can dabao food (like roast duck from the pasar malam) back to the room to enjoy in peace.

I like the BBQ chix wings from Cedar as they're still good (though cold) when eaten late night in the room.
If staying overnight, can choose to have breakfast in the many shops outside the hotel. Teochew porridge, roti prata/canai, wontan noodles, etc. Or one of the restaurants in the mall if you wake up too close to lunchtime.
And if you're adventurous enough, extend your room to 6pm @RM70(?), GrabCar to Aeon Tebrau in the morning and shop till afternoon and GrabCar back to hotel room. Still not enough shopping? GrabCar to the pasar malam near Giant Leisure Mall (~RM4) which opens at around 4pm already. It's shorter so you'll need lesser time there, and there's Mr DIY above Giant in the mall.