What are differences between these entities? I understand they all are entities that they posses some abilities that normal humans don't have. Are there any other similar entities that might be easily confused?
- Buddha is a completely self-enlightened one (without help from another Buddha, direct or indirect).
- Bodhisattva (in Theravada) is a being on its way to enlightenment.
- Bodhisattva (in Mahayana) is an awakened being who vowed to indefinitely stick in Samsara for the sake of others.
- Arhat (in Theravada) is a completely enlightened person (thanks to a Buddha's help).
- Arhat (in Mahayana) is person who has attained Peace (of enlightenment) for him or herself, but not willing to give it up for the sake of others.
- Deva is a non-human being invisible to the human eye.
- Sammasambuddha - Omniscient and has attained nibbana(enlightenment) on his own without the teaching of another. Preaches the Dhamma and guides other beings to Nibbana. Had cultivated Paramitas in three ways for a minimum period of "Sara(4) Asankya Kalpa Lakshaya" as a Bodhisatva. More than one Sammasambuddha cannot exist in the world at the same time. Always male.
- Pacceka Buddha - Not omniscient. Has attained nibbana on his own. Cannot preach the Dhamma that can guide others to nibbana. Had cultivated Paramitas in two ways for a minimum period of "Dwi(2) Asankya Kalpa Lakshaya". Many Pacceka Buddhas can exist in the world at the same time only if there's no Sammasamubuddha and no Dhamma in the world. Always male.
- Arahath - Not omniscient. Attained nibbana under the guidance of a Sammasamduddha and preaches the Dhamma to help others attain nibbana. Had generally cultivated Paramitas for a period of "Eka(1) Asankya Kalpa Lakshaya". This period may vary depending on if it's a normal Arhahth disciple or one of the 80 great Arahaths. Many Arahaths can exist in the word at the same time. Can be either male or female.
- Bodhisatva - A being who is still cultivating Paramitas to attain Nibbana through one of the above three goals. Can be either male or female.
- Devas - Not omniscient and not necessarily enlightened. They are divine beings who have done good deeds in the past and born in heavens as a result. They usually enjoy a long life span. Unlike humans, they don't get sick and don't deteriorate as they age until the last moment. Can be either male or female except for Brahmas who have no gender. They are born spontaneously.
All Sammasambuddhas, Pacceka Buddhas and Arhanths are similar in enlightenment with the above mentioned differences. There are no other similar entities to them.
Actually Paceccabuddhas do teach but in brief and in general terms like from one Theravada example after 4 Paccekabuddas received meals for 4 days from a King at his palace when the King asked them for a teaching they each gave a short sentence on one day, together it was: "Overcome greed, overcome aversion, overcome delusion, overcome restlessness." Notice the going from general unwholesome state to a specific probable personality problem of the King, restlessness. Aversion is anger, fear and sadness, a general term.
After each Paccekabuddha gave a brief sentence the King thought critically that brief statement was not very deep. But after thinking that again for on the 4th day he thought of all four statements and realized that their own teaching was deep. The early Hindu Brahman scripture the Rig Veda in a sutra from about 1000 BC talks about "recluse monks with soil colored robes who travel with the wind". Paccecabuddhas wear brown robes and use their psychic power of levitation to fly back and forth from their forest caves for their one meal. This is every evidence for Paccekabuddhas is Asia over 500 years before Buddha.
Thai Arahat forest monk Achan Mun who had psychic clairvoyance and telepathy took his hermit monk students for a group meditation to a large cave high up in the mountains of Northwest Thailand. He said that this had been the cave of a group of Paccekabuddhas. This is evidence that for over 500 years over a very wide area of Asian mountains there were many thousands of Paccekabuddhas.
I think that the ancient tradition of pre-Gautama Buddha meditating hermit yogis from Afghanistan to Southeast Asia very probably began with inspiration from the Paccekabuddhas. Thus the Paccekabuddhas are important in preparing the way for a teaching Buddha who teaches the full direct Dhamma (Dharma).