(1) the empirical formula C2H3O3 means that the molecular formula is C2nH3nO3n, where n is some integer. So for one mole of the substance there are 2n moles of Carbon atoms, 3n moles of Hydrogen atoms, and 3n moles of Oxygen atoms.
You've been given the total amount of oxygen atoms, if you convert this to moles you should be able to get the molecular formula from what I said above.
(2) The molar mass is just the sum of the masses of the atoms in the molecule, correct? You know you have 6x Carbons where x is some unknown, 5x Hydrogens, and 1x Oxygens, if you were to add up the atomic masses for the Carbons, Hydrogens, and Oxygens you will end up with a simple expression for the molar mass in terms of x, which you then solve for (given that you know the molar mass is 186)