Happy tear with no water
 

This black orchid has received no water (yet) but it is releasing sap. Is it normal?
It has had no first bloom yet because I got it as a seedling. When can I start watering?
The plant is in a 2"pot. When should I pot it up? Before or when I resume watering?

Quite normal. Take a look at the link that I posted to notes from Fred Clarke on spring care of Catasetinae - there are photos that should help you decide when to start watering. (That new little growth is a month to 6 weeks, at least, before it's ready)

Catasetinae Notes from Sunset Valley Orchids

As for potting, the time is already past - it is working on new roots. If you want to move it to a larger pot, you can slide it out of the current pot without disturbing roots, drop it into a larger pot and fill in around the sides with moss. (It will be damp but will dry quickly.) Next year, get on it somewhat earlier if you want to do a serious repot including cleaning up old medium. For this year, you can give it a bit more space, but don't mess with it.

I did merge your two threads on the same subject

Within the past two days Roberta posted here the Sunset Valley Orchids Catasetinae growing instructions for this season. Look up her post; it covers what you're asking in great detail.

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I would pot it up immediately. You don't want to let the new roots get any longer. I generally pot as soon as I see the location of the new growth, so I can judge the best orientation for the next year's growth. The new roots are VERY brittle and it is hard to work with them, so be cautious. However, if one is damaged, more will grow, so just do your best. The happy sap is fine. The plant is still a good bit before watering. See this post to judge when to start with the water. Catasetinae Notes from Sunset Valley Orchids

I know Fred's views on catesetum by heart.
Here are it's happy roots. Should watering resume now?
Yup I think potting up is what it needs.

I would wait on the watering until the growth is somewhat larger, and opening out. (You don't want to get water into the new growth) Just put into a larger pot, fill in with more moss around the edges, and then put your hands in your pockets any time that you are near the plant so that you aren't tempted to water it. (Catasetinae are a bad group for people who can't keep their hands off their plants...) In a few weeks you could moisten the moss around the edges just a little, but no soaking... That old pseudobulb is plenty big enough to sustain the new growth for some time with no water. That is what they do. It is not ready yet... look again at Fred's photos to tell you what the new growth should look like before you start to water.

Did these new fresh looking roots come from the youngest pbulb, or some "resumed" growth from the old roots of the older pbulbs?

New roots and new growth both come from that most recent p-bulb. (Prior year's roots may help with hydration but they're not very efficient, they don't continue to grow. After another year they are pretty much dead) The roots grow in anticipation of rain (water) not in in response to it. In Fred's talk about Catasetinae, there's a dramatic photo of him standing in the baking sun (in Mexico I think) with a huge clump of Catasetum with amazing new root system. He points out at that those roots grew without a drop of rain. So the pattern is 1. roots (anticipating rain) then 2. growth (anticipating rain) then 3. water . Water is LAST. Look again at the photos in Fred's write-up - the last 2 photos show what the plant should like before you start watering. Your plant looks like the ones at the very beginning of the series. Not even close to being ready for water.

Roberta's advice is right on the money. No water for a while and this plant is past it's prime for repotting. The media looks good so it would be fine for another season in that pot, but you could drop it in a larger pot and add media.

One thing that might disagree with Roberta is about those long roots with new tips. I think those are last season's roots that are continuing to grow. I've found last season's roots still growing on hybrids and that last season's roots are usually still pretty effective at absorbing water for at least the first half of the next growing season.

I think the longest root from the newest growth is seen on the far left of the photo where the roots are showing. Certainly too long for a safe repotting session. Honestly, I'd pop it back in the pot and repot next February.

Thanks everyone. I have gently potted it up without disturbing the original roots and moss. I think it is good for another year.