I haven't stayed at the property, but I can offer you some tips on transportation since I used to live a two minutes walk away from the property for 17 years.

Bus is more than doable, but don't take the buses on the Upper East Coast Road side since they're SLOW and they meander through the small and/or slow roads. The buses on the Marine Parade Road side (facing the Mercure is/on the way to Parkway Parade is) are much faster. Bus 36 and 48 in particular takes the expressway. Bus 36 on the Parkway side would take maybe half an hour to Suntec City (that's its first stop off the expressway), and it's relatively easy to get around via MRT on the Circle and Downtown line from there. It heads into Orchard via Dhoby Ghaut too but I tend to feel changing is faster. Bus 48 will get you direct to Bugis (also about half an hour, same expressway) and Little India and all the way to the Botanic Gardens and Holland Village, but for those I recommend you change to the Downtown line once it gets off the expressway and stops at Bugis MRT. Clarke Quay is pretty doable via the North-East line when you alight at Little India.

Bus 36 on the side of Marine Parade Road nearer to the Mercure would head you straight to the airport (and takes the expressway too). I generally found Grab/Taxi not really worth it for the places you want to go (except Clarke Quay), since they take the same routes and don't offer too much of a time saving unless you really can't endure the possibility of standing during peak hour and/or the three/four bus stops the bus takes before heading up the expressway.

​​​​​​The good thing about the property is that the entire Joo Chiat/Peranakan district is at your doorstep, and the famed Katong Laksa too. And one of my favourite ice cream places (Birds of Paradise), which ranks up there with Intelligentsia in Eindhoven for me.

Of course if you can wait till 2023/2024 the new Thomson-East Coast line will make things somewhat faster!