The border lines between want and need are pretty flexible. Although modern English tends to relegate want to a more specific meaning, you'l still hear "he was found wanting", or "for the want of...", both meaning that a person was missing something important, rather than they just wanted something.
In Welsh, they are more flexible, with eisiau being anything from needing to wanting to missing something, and angen being more needed or essential. Moyn, from the word ymofyn, which is "to ask for one's self", can be to want or sometimes to fetch. So, try not to think about the words as absolute translations of the English words, because they really don't always work in the same way.
Because of this flexibility, the northern isio doesn't sound that foreign to a southern ear, although I understand that northerners find moyn a bit more of a challenge!
There's loads of tags that get used. We go with on'd ife? (onid yw efe? - isn't it?) on'd oedd? (wasn't it) and on' bydd? (won;t it be) in the southern course. The Llandysul tag is "no?", which despite me turning into a Cardi in many things, I still find lovely but totally foreign to me!
A bit like hearing a proper Valleys Welshman saying "isn't it?" at the end of any sentence, you can get away with "on'd ife?" after just about anything. "But you'd happily do that, isn't it?", but you can also just repeat the verb at the end of the sentence.
"Gwneiff e hynny i ni, (on') gwneiff?" - He'll do that for us, won't he?
"Bydde fe'n gwneud hynny, on' bydde?"