Cyrillic for English - (Сарилик фоьр Иңглиш) is an adapted Cyrillic orthography to write English using ь as schwa, so 'sofa' would be written 'соьфь'. Does ь make sense as a schwa or is ъ better? The way I understand it ъ basically forces a pause. Is there really any use for ь or is there something I'm not understanding about how they are used? Is there a character that would make sense to use at the beginning of a word?
If you're going to use one of <ъ> or <ь> to represent /ə/, it's probably better to use <ъ>. This letter is currently used to write /ɤ/ in modern Bulgarian, whereas <ь>, as far as I'm aware, is only used to write actual vowels in dead Slavic languages. Moreover, because <ь> historically represented a short front vowel, it is used in modern languages like Russian to indicate palatalisation, something that does not accompany /ə/, whereas, e.g. in both modern (and more widely in pre-reform) Russian, <ъ> marks not a vowel but the absence of palatalisation.
I'd use neither ь nor ъ because they aren't vowels in Russian or related languages. I could think of Ы that is a vowel and may be the closest by pronunciation, or of Э that looks a bit like a schwa. In extended Cyrillic we even find a true schwa Ә but this one may be out when we have only a Russian Cyrillic keyboard available.
<ъ> is used to write /ɤ/ in modern Bulgarian (some of which are non-etymological). <ь> and <ъ> were also used to write "ultra-short" vowels in some older Slavic languages, e.g. Old Church Slavonic and Old Russian. – Miztli Oct 30 at 10:07
But Ь is not used for a vowel in all Cyrillic languages.