Hello Ryokan!
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Well, this is great! =
-Yah, ini hebat
Well? You coming or not? = So? You coming or not? =
-Jadi? Kamu ikut atau tidak?
-Jadi bagaimana? Kamu ikut atau tidak?
"Jadi" or "Jadi bagaimana" are very suitable for those example.
May be you could give some sample sentences for me to translate the meaning?
Hope that answers your question. :-)