ツ好窶堋ォ窶堙遺?堋セ窶堋ッニ坦ツーニ智ツーヒ?ケ窶堙ア窶堙??堙?窶堋「窶堋「窶堙ヲ is more focused on the amount that it's OK to drink at that moment in time, right? In that case I'd say "you can drink/have as much coffee as you like." I feel like "have" would be more common here, actually. I'm not sure if it actually is, or why I feel that way, though.
Now, a) and b) are more like "you can drink coffee as often as you like," and they focus more on occasions than quantity to me. So they'd be more like ニ坦ツーニ智ツー窶堙ー窶堋「窶堙や?堙??堙?ヒ?ケ窶堙ア窶堙??堙?窶堋「窶堋「窶堙ヲ or something like that, I guess.
I'm curious to see what other native English speakers have to say about this.