SpaceX is producing about 5 Merlin engines per week and has the factory capacity for 400 engines per year or about 8 engines per week. The Raptor engines are about the same size as the Merlin engines. The new BFR and BFS design needs 38 Raptor engines. SpaceX should be able to build about six to ten BFRs every year even without building more factory capacity.
The BFR spaceships (second stage) will be reusable, Musk plans on refueling them in low Earth orbit first, and then again on the surface of Mars for their return to Earth.
They will launch several BFRs to transport and assemble a propellant plant and start to build up a base. The propellant plant would produce methane (CH4) and liquid oxygen (O2) from sub-surface water ice and atmospheric CO2.