For my part, I would want to wear a half head covering, go in non-tight pants, and wear a short-sleeved T-shirt. In the ulpana they taught that this is forbidden. If it is permitted—then I want to, because it’s more comfortable and enjoyable and airy and pleasant.

In your opinion, am I allowed or forbidden?
If these are disputes, there are lots of things that are disputed, and the rabbis decide what the Jewish law ultimately is. Like the time for reciting Shema, whether earlier or later, where there are two views..

Rabbis don’t decide anything. Only the Sanhedrin has the authority to decide. A rabbi is an expert in Jewish law, and if there are several opinions he is supposed to present them to you. He can of course add what seems right to him, but if you do not accept him as your authority, you are not obligated to follow his opinion.
If we are talking about pants that women also wear, I do not see any prohibition in the matter, because it is not men’s attire. On the question of modesty, use common sense. In any case, with non-tight pants I do not see a problem.