You will not really be based in Jeddah, in reality you wont have any base at all and these days the majority of flying is outside of Saudi primarily from LGG, FRA and HHN.
The company will arrange travel from your nominated domicile to wherever they need you and home again as well as all accommodation in hotels when on base.
You can expect to upgrade to FO after 500hours on type (and when the next course comes around) which is something like 12-18 months.