It may be better to use future tense rather than conditional: "That kind of thing won't work", "Something like that won't work". Then it's just a special case of the general principle that English often marks futurity explicitly when Dutch doesn't. (Of course there are situations in which the Dutch present tense is meant literally and should be translated as present tense.)
If you use conditional (in Dutch or English), you are implying that it's not being tried yet.
They are almost identical they can probably used interchangeably in most cases. But I think that dat werkt niet refers to the exact action or approach that does not work (changing it a little bit could work), while zoiets werkt niet is a bit broader and refers to any similar action or approach won't work. Basically is't using that vs. something like that. I wouldn't worry too much about the difference.
- Ik wil deze verf van mijn handen krijgen met wasbenzine > Dat werkt niet, maar met terpentine wel. = I want to remove this paint from my hands using benzene > That won't work, but using turpentine will.
- Ik wil deze verf van mijn handen krijgen met wasbenzine > Zoiets werkt niet, je kan het er alleen af krijgen door het eraf te schuren. = I want to remove this paint from my hands using benzene > Such a thing won't work, you can only remove it by sanding it off.
For starters, "such" in the sense of "that sort of" is much less used in English than Dutch people think it is. Many phrases with "such" will sound strange, and something that might otherwise be a borderline accepted variant is now a rare variant of an already rare sentence.
Beyond that, just as the dutch default is to treat "beer" as un uncountable noun (much like water), so Americans treat coffee (most of the time). Could be because so much traditional American coffee might as well be hot, brown water (LOL) and it's often offered in the form of a "bottomless cup" that gets refilled endlessly unless and until you tell the waitress to stop filling it.
You can make an argument for using the "a" with coffee, but you have to first create a context where it's a singular item. OK: "They make the most perfect espresso--the cup is tiny, the crema is perfect, there's a tiny sugar cube and a twist of peel alongside. I love such a coffee." That way, you're setting it up as "a coffee, the single distinctive serving," not "coffee, the brown liquid with caffeine."