Regarding the Buddhist ideal model for practitioners, is there any difference between Southern Buddhism and Northern Buddhism?
I could see some similarities in the Theravada Mahayana Doctrines.
Mahayana and Theravada
Both rejected the idea of a supreme being who created and governed this world.
The Four Noble Truths are exactly the same in both schools.
Both Mahayana and Theravada doctrines help us to not being influenced by the objects of the six senses. In Mahayana they call it the becoming of Buddha Nature – to be awakened. We call it being an “Arya Shrawaka” in being a part of the ideal community of Noble Ones (ariya-sangha)
The Eightfold Path is exactly the same in both schools. ‘Paramita’ in Mahayana is this ‘crossing over’ and ‘reaching the other shore’ in walking the eightfold path.
The Paticca-samuppada or the Dependent Origination is the same in both schools.
Both accept Anicca, Dukkha, Anatta and Sila, Samadhi, Panna without any difference.
Buddha discourages reincarnation in any form stating he wouldn't, even for a moment, praise reincarnation. Yet, unlike in Theravada, in Mahayana one seeks strives to become a Buddha through reincarnation.
Becoming a Buddha, or bodhisatva isn't something Buddha has encouraged (according to Buddha Jayanthi translations of the original teachings of Buddha)
By Northern Buddhism, if you mean Mahayana Buddhism and by Southern Buddhism, if you mean Theravada Buddhism, then yes there are some differences.
Theravada Buddhism talks about the Four Noble Truths etc. And while Mahayana also talks about them, Mahayana adherents are taught to transcend even those doctrines. I am unsure if this is only peculiar to the Chinese Mahayana Buddhism (where I came from). A popular Chinese Buddhist scripture, the Heart Sutra, emphasises on Sunyata or "emptiness" (空). For example, the Heart Sutra mentioned that the Four Noble Truths are "empty". (无苦集灭道)
The goal of Theravada Buddhism is to be an Arahant, while the goal of Mahayana Buddhism is to be a Bodhisavtta. The difference between the two is that an Arahant focuses on his or her personal enlightenment while a Bodhisavatta focuses on the enlightenment of all sentient beings.
Do note that I'm more familiar with Mahayana compared to Theravada. And I'm no expert. Feel free to criticise and comment my answer.