Here are my answers to Hope Rainbow's questions:
(1) Buddhas can help followers to achieve arhatship or Buddhahood through their teachings. During the Buddha's time, many of his followers became arhats. However there is a difference in the goal of different Buddhist traditions. In Southern Buddhism, the goal is arhatship or individual liberation because the belief is that there is only one Buddha in any given age, so the best one can hope for is arhatship. In Mahayana Buddhism, the ideal is the achievement of Buddhahood for the sake of others. Thus, achieving only arhatship is not enough because one will be of only partial benefit to oneself and others. An arhat has not abandoned all that has to be abandoned or achieved every good quality. Later,the arhat will have to enter the Mahayana path at its most basic level. This is like entering the stream twice, thus wasting a lot of time. Thus Mahayana masters would encourage the practitioner to enter the Mahayana at the outset and strive for Buddhahood.
(2) Arhatship is easier to achieve. Both Mahayana and Southern Buddhism recognize that the path of the arhat is essential. Both arhats and bodhisattvas go through the first six stages on the path to enlightenment, cultivating wisdom. While the arhat is stuck at stage six, the Bodhisattvas move on to stages seven, eight, nine, and ten.
(3) I agree with this view.
(4) No, although it is easier to achieve arhatship, it is still better to enter the Mahayana path at the outset because one achieves full enlightenment faster than the arhat who, even after being roused by the buddhas from their blissful absorption, will find it very hard to develop bodhicitta. The danger for the arhat is that he/she is stuck at stage six of becoming "enchanted by the bliss of the samadhis" and thus "pass to their nirvana" without completing the path to full enlightenment. In the Lamrim, it is said that they stay in this absorption for many eons and have no wish ever to leave it.
(5) There is no doubt that the ideal of the Mahayana is the better choice. For example, Manjushri was praised by the Buddha for his skillful means when he taught 60 monks Mahayana Dharma before they were given Hinayana teachings by the shravaka Kashyapa. This was to make sure they did not become arhats and become stuck in this path. The two major disciples of Buddha, Shariputra and Maudgalyayana, said, "The Teacher has taught both the Mahayana path and its results. These are most wondrous, but we are like wood already consumed by the fire: we could not have done more." According to Pabongka Rinpoche, this does not apply to people like Shariputra, because they were emanations of buddhas taking the form of shravakas. (Liberation in the Palm of Your Hand, p. 501)