Yes, if you do not have a gamedata folder you can make one.
As far as multiple mods go, it depends. As long as the mods don't change the same files you will be fine. If you are familiar with oblivion mods, as it sounds like you are, then you would be familiar with this. Certain mods are not compatable with others becasuse they change the same file differently. For example a mod that changes the AK damage and a mod that rebalances many weapons, including the AK.