This is quite a difficult one to answer, cos you can't just make a comparison between one opiate
and another like that. Usually people (in the UK) are started on 20-30 mls and this rises by 5-10 mls (depending on your doc
worker) every 4-5 days. This is because it takes that long to see how the person feels once the methadone
has accumulated in their body. Basically if you get an increase in dosage on one day, it won't be felt like it would if your dose of oxycodone
So I'd suggest taking the doses that are offered, and as it rises see how you feel, cos that's the bottom line isn't it, how comfortable you feel, and how manageable your life is? You'll know when you're at the correct dosage for you, cos you'll have no WD symptoms, and you'll feel stable on your dose. As for how often you should take it, again in the UK it's given as one daily dose, which seems to work due to the long half life of this drug.
When I was prescribed methadone I've actually missed a daily dose, and not even noticed it. This is why methadone is perfect for anyone who is looking to stabilise and perhaps quit opiates
in the future, cos it holds you on one dose a day. And it enables you to sort out any problems you may have without having to run your ass off to score, or take multiple doses of another prescribed opiate. One dose and that's it, you get on with your day.
If you are looking to eventually quit I suggest thinking about why you needed to use an opiate in the first place, cos usually when people just put down a drug and don't deal with the reasons they became addicted, they usually end up relapsing. So it's important to plan your quitting, make sure you have enough support systems in place, kinda like safety nets to catch you when you fall. I say when, cos we all fall, but that doesn't mean we can't pick ourselves back up, without actually using.
If you intend to stay on methadone long term then I also suggest staying away from other users, as you might be tempted, cos methadone doesn't produce that euphoric high that most other opiates do, it just kinda mellows you out and stops you from getting WD symptoms. Lots of people are surprised and miss the high. That's when you need to keep yourself safe. It's also good to get rid of all dealers numbers too.
Try to get into a lifestyle that enables you to deal with any problems you may have. I found it excellent for this. Cos I had emotional problems that needed to be dealt with, and on methadone my life became stable enough for me to do this. That meant that the reasons I'd used opiates in the first place were no longer present when I quit methadone. That gave me a much better chance of staying clean, cos there were less pressures.
Hope this helped a little. If there's anything else you need to know please, don't be afraid to ask. You can always PM me, and if I can, I'll be more than happy to help.