I don't really see Zen as a Buddhist practice Dharma wise. I think that after 3-4 years of devoted Theravada practice someone would be in a developmental position understand and to deal with Zen practices. Zen is rigid practice and personally the most destructive Toxic personalities I have ever met were long time Zen practitioners. I first ran into Zen before I knew anything about Buddhism, I was so devastated by them I quickly decided Buddhism was a bunch of crap populated by psychopaths. what I had run into were Dharma Bums. I later found different groups, but they still reeked of their militaristic past, they hit you with sticks if you don't do it right..
20 years after my first run in with Zen I met a Tibetan monk, it was like coming home after several lifetimes of being lost., he had been the chant master of the Dalia Lama's monastery, and an attendant to the Dalia lama. I attended three 3 hour meetings a week for 6 years, never missed a meeting, 2 were on meditation. his first advice was to start at the beginning. to learn Theravada first. start with the 4 Noble Truths. they are the foundation of Buddhism.. they ARE Buddhism. they are a simple logical Posit. everything else in Buddhism is an effort to understand them.
start here, they are a Theravada group and have a good beginners program and are a solid traditional reliable resource, they have meditation training video, on Vapassina and later Shamata.. check out their Buddhanet Audio pages for really good teachings.
www.buddhanet.net
I love this video..