So I presume that "Roxicet" implies oxycodone and acetaminophen, correct? We don't do pill ID's here.
Anyhow, given the assumption of the inclusion of APAP - don't eat more than 1g of APAP at a time (probably 2-3 pills assuming x/500 or x/350), and no more than ~3g per day otherwise you risk liver damage.
Do NOT insufflate APAP.
Can't give a dose recommendation given you haven't listed any experience / tolerence present, so start with, say, 10mg of hydrocodone tops and go from there a different day.
If you are going to be taking more than the aforementioned amounts of APAP, I highly suggest that you CWE (cold water extract) the opiate from the pills to leave most of the APAP behind. Search around for instructions on that - quite easy to do.
Oral BA of oxycodone is higher than nasal by a decent bit. Not sure about hydrocodone, but (the information is somewhere) I expect it to be similar. the -morphones are opposite though, and have awful oral BA's. (BA = bioavailability, or how much (in % ) will be absorbed by the body for use.)
Regarding benzos - none of them are more effective nasally (for the most part, some can be insufflated with positive benefits of course).