If you read things that are in kana only, or that have furigana, it shouldn't be a problem to learn them.
The おお versions are fewer due to historical reasons. They come from words that once either had an interpolated "w" or "h." For instance, とお ("ten") was once actually とを, and とおい ("far") was once とほい.
The おう versions went through various changes, like あう -> おう, えう -> おう, えふ -> おう, おふ -> おう, although really the kana probably reflects an older pronunciation, but it's still spelled that way.
There are also words where the sequence is pronounced as it's spelled, like 負う/追う (おう). In this case the う is actually the verb ending, and at one point it was most likely actually "wu."
Anyway, unless you really plan on studying etymology, it's best just to take it on a case-by-case basis, with the assumption that most of the "ô" you come across is "(X)ou" (where X is any consonant, including a null consonant).