Good news tt you drive all the way to Qatar most welcome. You should complete visa process especially saudia ( via road ) you can get in abudabi saudian embassy or some ageny there. when you reach Qatar border there is only immegration process and they will come and chk ur car and the persons (how many) with valid documents. after reach in Qatar you start process easily for the registration ,insurance,driving licence ect....nowadays it is very easy system we have in qatar for the process of whatever govt related work. You need Insurance while driving between Abudabi to qatar. all the best