If it's based on a silent vowel, does that make this useless information unless we're paying close attention to vowel signs in a text written with vowel signs? Does that mean one just has to memorize words that take it?
Or does this 'silent vowel' mean when we have two consonants together at the beginning of the word, like 'sm' in 'smichah'?
Well, as the rules apply to older stages of the pronunciation of Hebrew and if you want to speak formal Hebrew, you would have to remember the affected words. If you slacken your precision a bit, you could at least use [u], when you hear a double consonant, which would still be posh.
No, in English you don't always need the indefinite article. "I need pillow and blanket." is proper English too. One citation saith thusly "Non-native English writers commonly either omit or overuse articles. Articles are not always necessary. Articles are generally not used when referring to an entire category, such as education, patience, music, etc. " (scitechedit DOT com / en-GB / helpful-resources / white-papers / the-use-of-articles-in-english-writing) Yet is more flexible than even that.
For example a mom might say to a young'un: "To go out, young wee bairn, you need hat and coat." Not "a hat and coat" or "a hat and a coat". Just "hat and coat".