Methadone is powerful, long lasting and it accumulates in your body. There is a very big difference in acute (once weekly) and chronic (every day for 3-4 days until steady state is reached) potency of methadone. To make things even more complicated different people metabolise methadone differently and difference is very big and measurable. There were cases where people died of 20mg methadone, if they did not have opioid tolerance and took methadone few days in a row. One more very important thing - don't use any other depressants with methadone. Taking benzodiazepine (Xanax/Valium/Klonopin...) with methadone is the fastest way to not waking up without even realising that you are overdosing. Also things like alcohol, pregabalin, phenibut or some other CNS depressant must be avoided if one is taking methadone. It is a very tricky and for opioid naive person (or very low tolerance) very dangerous opioid to take.
Having said all that, as others said, take at most 20mg - and lay off for a week. Forever would be better but I will not preach. I wouldn't advise more than 10mg and then pause for a week. Than try 15mg and wait for 2 weeks. Than, based on your response maybe go as high as 20mg. But methadone is not "in your face euphoria" like oxycodone for example. It has it's place but , in my opinion, not for recreational purposes of non tolerant people.
Proceed with great caution and take care!