Master sheduling (MRP)on the one of the added dimension

In standard AX 4.0 how many Dimensions are there in the dimension tab of the item master?

upto how many more dimension MS can provide?

can we run Master sheduling (MRP)on the one of the added dimension?

Presuming it is financial dimensions they provide 3. There is no limit, but you pay for each. There is probably a restriction on performance, but I am not aware of it. It is not advised you run MRP with any filter, you run it THEN apply the filter, otherwise required related supply would be missed.

which are the default three?

Is it not advisable to run by filtering even with one of these default dimensions?

The three standard are department, purpose and cost centre, but the names are irrelevant you can rename them with a simple modification, the point is you have three. Yes never filter planning by one of these dimensions.