Tentatively in + 1 for the brunch. Will confirm asap.

As for what to do after the brunch - depends on just what levels of rowdiness you want to experience. In order of least to most, a few suggestions:

Stay at the PH for more drinks at The Terrace, overlooking the Creek
As KU104 mentioned, upstairs at Zuma
Atelier M
360
Jetty Lounge/Rooftop at One & Only
Calabar at Address Downtown - overlooking the fountains
.
.
Barasti
Irish Village
Double Deckers