Skud Run, here goes.......
1. FZ will give you the cheapest routing to DXB. If that stops over in desirable places or undesirable places, that's pot luck. Whether it's direct or not is also pot luck. They'll try to get you to DXB using FlyDubai and if they can't then the next cheapest thing going. Don't bother trying to 'request' anything different, even if it makes sense to you. The company will do what makes sense to them (that means whatever is cheapest normally). So homebase to DXB only.
2. Your family are eligible for their jointing tickets anytime you're ready. Most people (and have many company personnel) advise on bringing family out once your type rating/training is done. Remember, anything can happen. Most people I speak to bring their family out after training is done.
3. Your 5 year old is classified an infant hence will not get his own seat. Lap only.
4. Someone else may have to chime in here. It's been a while. I know FZ give money towards relocation (it's a nominal amount - would have to be self subsidized), but whether that can be used toward extra luggage, I'm not sure.
Hope some of that helps.