It all depends on how similar to the animals you describe you want this creature to be.
First go the easier part, the eyes of a deer, practically no problem here, is the most probable case that an herbviore animal have the same kind of eyes. With horizontal pupil to increase the lateral vision range. But I understand how the deers having thin and little heads is related with the kind of eyes.
Next, the comparission between rhino and horse is pretty correct, both are part of the same mammals order, Perissodactyla.
Nevertheless a better comparison for the rhino is the tapir, much more related with the rhino than the horse.
And the plus for this strecth phylogenetic relation, tapirs have trunks.
So the next is easy, a tapir or other creature with a body plan similar to the tapir's body evolves in the same way as proboscideans did. The elephants ancestors were very similar in the external appearence to tapirs, like Moeritherium, as they evolved fangs and trunks these creatures evolved better trunks and horns, the horns can be justified as defense or intraspecific combat.
I think the idea about add the elephant skull shape with the humanoid shape is hardly useful for this creature model an harmful for all the other features.