Questions:
1. Does each engine has accessory drive attached fuel suction pump?
Yes a HP and LP pump or First and second stage.
2. If so from where does this pump suction fuel from - where is the pump's inlet connected?
The pumps inlet is connected to the same pipe from the tank where the boost pumps are connected there is just an additional pipe that bypasses the boost pumps.
Can engine one suction fuel from any tank?
Technically yes but realistically no, Boeing doesn't say yes as it probably won't work as it would have to go via the crossfeed system.
3. Does stab tank really has boost pump, since the symbol for pump (on secondary EICAS under FUEL) is the same as for overide/jettison pumps and fuel is also fed from this tank in fuel jettison operation?
They are Transfer/Jettison pumps same as the Override/Jettison pumps.
Will have to double check the MM though.
4. Where does stab tank fuel outlet goes (they are only pictured when fuel jettison is armer)?
To the center tank.
edit: Except during jettison then fuel goes to the jettison manifold.
Can stab tank pumps provide fuel to the crossfeed manifold as other boost pumps?
No it just fills the CWT therefore you have to wait till the center tank is below approx 36.5T (edit: as above).
5. What is a vented surge tank?
Should a tank become full due to over fueling or expansion of the fuel it will be forced into the surge tank, should this tank fill, it will come out the vent, normal ops means the vent a NACA duct provides a positive head of pressure to all the tanks. Air pressure has to be able equalize inside the tanks ie as fuel is used air needs to replace it in the tank this is done by the NACA duct and via the surge tanks as they are connected to all the tanks.
6. Can fuel from reserve and outboard tanks only be gravity transfered to inboard tanks?
Yes from the reserve tank as there are no pumps. The Outboard to inboard transfer is by gravity and only during jettison the outboard tank may still be providing fuel to the engine and crossfeed manifold via it's boost pumps.
7. What is the scavenge pump flow and is it AC or DC powered?
I'll need to get that from the Maintenance manual.