A 3 week cycle is pretty short and you probably wouldn't need an anti-e like 6oxo post cycle, but it would help you maintain your gains better than not using it. But you don't absolutely have to have it. Vitex is used for prolactin suppression which can help if you start to get progesterone gyno. Which would be rare to get from 1-test, so you probably don't need this unless you start getting some puffy nipps that won't quit.
Otherwise, add a high dose of to your post cycle and you should be fine. 6oxo is optional.