One of the problems in using a TEN tip to practice with acetylene is that it is probably the wrong orifice size. A Victor #0 or #1 tip is what I would be using to practice with oxyacetylene and a TEN-2 or TEN-3 to practice with propane. It would be one hot flame using a TEN-2 tip with acetylene that would require faster reaction time to keep the joint within the proper temperature window. When one is learning how to braze they have difficulty reading the heat indicators and then adjusting the flame fast enough. For learning purposes, it is better to start with a smaller flame so things heat up more slowly and it is easier to understand the heat stages the joint is going through.

To specifically answer your 1st question I do not know if a TEN tip works with acetylene. I wouldn't use that combination myself as I have all the right equipment. My suggestion - if you already have the UN-J mixer/elbow - is to get the TE acetylene tips (not to be confused with the TEN propane tips) designed to work with a UN-J mixer in a #0 size to start out with.

To answer your other question is that a TEN-3 tip is the one I most commonly use with propane (compared to a #1 with acetylene). I can use that tip for almost everything. For big stuff like fork crowns to steerers, I use a #4 and little things like braze-ons I'd use a #2 (if I am ambitious enough to change the tip).