The best thing about baking with yeast is that the quantities of the ingredients are not as critical as other baking.
You can experiment at will (within reason) without worrying to much. If you add extra flour or sugar or water your dough will still rise the yeast will just have to work a bit harder not you.
Altitude does not really effect baking, except that at higher altitude your dough will rise quicker. The taste will not be effected either.