Vias size for heat transfer on copper pad on both layers

[Vindhyachal.takniki]

1. I have designed a circuit with 10A of current capacity. For large current I have made large copper track on both top & bottom layer. Now to connect both tracks, I have made multiple vias of size
drill dia: 23.62205 mil
pad dia: 39.37008 mil

Vias are connected so that heat can be transferred between both tracks equally on top & bottom.
A)What is the ideal vias size for this kind of purpose.
B) I have found one chinese PCB, they have vias spread acorss track. What is size of vias in attached pics?

2. I have attached gerbers EVM of bq24650. On top layer it has IC bq24650 with 9 micro vias benath it. What is tehre size. I think it is 0.010 inch as mentioned. Is it tht small?
What is drill & pad size for this via?

3. I have to design a heat sink for PCB. On locla market I have it just a Aluminium which has been tooled for this purpose. But on internet I was reading heat sink are of particular AL alloy. Does that mean I should get it tooled from some reputed manufacturer only?
AL alloy have better thermal conductivity but do they have better thermal dissipation also?