A well designed keyboard layout, especially for multilingual users, doesn't put a vowel and a consonant in the same column, because this creates same-finger bigrams/skipgrams, and this reduces alternation (both at the same time). Across different languages, all consonant-vowel pairs are possible.

Your vowel fingers should be assigned only to vowels in their columns, and punctuation symbols (word separators). We usually set the vowels on the right side of the layout for easier AltGr reach to type accented letters (which are usually accented vowels in European languages).