I would say Wizard 1-10 with them getting spell levels on every odd level (so at level 19 get level 10 spells)
I would want Clerics to get level 1-7 getting them every 3 levels, so 1st, 3rd, 6th, 9th, 12th, 15th,and 18th
Give them almost no class features (I said almost not none) then you can...