A: 
Hi Noah,
I am a Tibetan medicine Doctor and professional only in this field, therefore I can only give you Tibetan medicine related questions such as concerning the medicine Buddha. But your question is very interesting and I would like to explain to you roughly what I understand about the various Buddhas.

Buddha Maitreya (Sangye Jampa), Buddha Dipamkar (Sangya marmey zey), Buddha Amitabha (sang gyy voe pak mey) and Buddha Sakyamuni (sang gye shakya thubpa), etc. directly appear on earth in the human form as human beings, one after another.

Some Buddha emanations may be in the form of a statue, or speech, mind, attributes and activities, for instance, the Tibetan Medicine Buddha (BHAISHJYA GURU OR VAIDURYAPRABHA). The original teachings of this ancient Tibetan medical system are generally attributed to the Buddha who is said to have taught the root of the tradition in the manifestation of the Medicine Buddha. He influenced the rGue-zhi or four Tandras which is still practiced throughout the world.

Dr Namseling