bro.. i faced similar situation just like you..head big big when i switch to that plan.. i did call up several times and ask them 1 by 1..

1. optimiser will kick in automatically if finished either one of the call/sms or data..you will get sms notifications saying the plan has already been optimized.. and confirmed optimized 1 time (either data or sms/call) on each month nia..

2. it will reflect all in your bal status for all your entitlement + if you bought additional data volume in the same month..

3. all their celcom first postpaid plans are non PPU basis.. everything will get throttle speed whenever data finished, no matter what plans you are on. the only ppu is the call/sms if you finished up the complimentary one lo.. haha

4. ya it will carry forward to next month if you cannot finish utilize your data depending how many gb you entitled for the plan you've subscribed.. it will appear in bal status too.