I rather have the 100 B5Ls to be Mercedes-Benz Citaro 3 for
SBST, unless there is a 3 axles version of the B5L. 100 Scania
K310UDs will do. Another 50 for E500 bodied Volvo B9TL
For SMRT, most likely there will be more MAN bus since SMRT is
switching to MAN.
So.
- 50 Mercedes-Benz Citaros (EvoBus GmbH)
- 100 MAN A22
- 150 MAN Double Deckers
Fully agreed.
Talking about SBS997A, it think this year is its last year.
Don't know will there be extensions given to it. 
The fleet I hoped for SBST is talking mostly about double-decks,
unless if I replaced it with Volvo 7700 (single-deck version of
B5L), then you can consider Citaro 3, but I still won't accept more
Citaros other than those ordered in 2010.
As for B9TLs, I think it is too much to purchase so many of such
buses. Why not I suggest Alexander Dennis Enviro400 (a complete
bus) instead?