You'd probably have better luck using the search engine for this question rather than a whole new post. Also, if you google "opioid conversion chart", you'll be able to find websites that convert different opioid dosages from one to another. 120 mg codeine is probably a fine dose for beginners, but you didn't mention how much percocet you usually take and if you have a tolerance or not, which also factors into it.
Codeine tends to be more of a body high for me than oxycodone, the latter tending to be more of a head buzz. But for people who aren't widely experienced with alot of opiates, most opiates will feel more or less identical, and indeed, they do feel very similar, with only slight variations on the same theme with different opiates.