1. yeah they should be fine. if they've been out in the heat, or got damp, or haven't been sealed in blisters or in a bottle then it's possible they might have degraded.. but they are not likely to do you any harm at all and i would imagine they shouldn't even be weakened (disclaimer: nothing is 100%, if they look odd then throw them out!)
2. your height and weight have v little effect on dosage; it's all about your tolerance. you're right in thinking your tolerance will be zero given your history, but natural tolerance can vary quite a bit.. do you know what dose of codeine you took in the past? if so check out the opioid conversion chart in the header at the top of this forum to work out your approx oxycodone dosage; i'd err on the low side as oxy is a strong opioid. if you can't remember, then i would take 5-10mg for your first time, definitely no more than that. it's far better to start really low and not feel much the first time, and titrate up, than to overdose..
remember not to mix it with any other cns depressants (alcohol, benzos etc) and take an antihistamine if you get itchy. enjoy!