One of the things that you could do to get the feel of how much pressure is to take a kitchen scale that weighs in grams, and weigh your razor. Then take your stone, place it on the scale, tare the weight so the scale reads zero with the stone on it. Do a few strokes on it while your stone is on the scale and try to stay within the weight of your razor but no more than +50%. That will give you an idea of "weight of the razor" pressure.

However most of the time it for me is, when using a stone holder, just enough pressure to make a good contact with a steady stroke. But usually I use shooter's advice on hand honing. You get a good feeling of what pressure you are using and it almost forces you to use lighter pressure and almost any inconsistency of your stroke is compensated for by your other hand holding the stone.