They're called schwa and wedge. This is actually a discussion I've had (not particularly fruitfully); schwa, being a reduced vowel, is sort of notionally only available in unstressed syllables. So you'd want to say a stressed syllable uses the wedge. But indeed they don't seem to be pronounced differently for many people, or at least not differently enough that there's an obvious answer. Merriam-Webster seems to use schwa even for stressed syllables like "stuff".

Twenty to twenty-eight. Depends on the accent and dialect. Of course, it can be a different set of twenty-eight in different contexts, depending on accent and dialect.

"Is there really a difference between "backwards e" and "upside down v"?"

Not in Utah.

"English has much easier grammar than Spanish"

I don't really agree. English uses phrasal verbs instead of reflexives and circumlocution in place of most subjunctives, but they're just as complicated.