Nope. U can take bus direct from probolinggo to surabaya, only 2hrs each way

Why complicated pulak? 
You flying to Surabaya then to Bromo right? One week more than enough, you only need one full day in bromo to see most of everything 

Your itinerary like how? Fly back to Malaysia from where? No need scared la, Java is quite well connected. If not sure, just ask

Anyways, up to you, Yogyakarta also quite interesting. But Bromo is too awesome to pass up if you're in Java 

1 week more than enough to cover actually

D1 - Jakarta
D2 - Jakarta. Night train to Yogyakarta
D3 - Yogyakarta
D4 - Yogyakarta. Afternoon train to Surabaya.
D5 - Surabaya to Probolinggo to Bromo.
D6 - Bromo. Back to Surabaya
D7 - Fly back

Up to you. You can take the night train to Surabaya if u want to save on accommodation. But that morning when u arrive at Surabaya, you need to get to bus station to get the bus to Probolinggo. From Probolinggo bus station, u can take the minibus to Cemero Lawang.

Cemero Lawang itself nothing much to do, though u can hire an ojek to bring u around to see bromo savanna, sea of sand or even visit bromo crater in the afternoons.

sound like a plan