One thing is sure : if you take MDMA one night, don't take MDMA in the following weeks (at least 4 in my opinion, but sometimes I can accept a little MDMA).
Concerning the amount of MDMA, it depends on your tolerance.
If you have never taken MDMA, an amount of 0.10-0.15 is good. If you have already taken MDMA few times, you can take an amount between 0.2 and 0.3. If you have taken MDMA several times, you have a high tolerance, so you probably need more than 0.2-0.3 to enjoy (because the tolerance reduces the effects intensity)
but
if you are in the 3rd case don't be stupid and set a limit, because MDMA can become dangerous if you are close to 1g in one night, 0.5 is already a high amount of MDMA.
For example, I have taken MDMA so many times that I have a high tolerance and now I can take 0.6 without being close of the overdose. I did it last week and I had no hallucination or any bad feeling (I was careful towards the dehydration and I drank lots of water, as always), it was a good session, nothing crazy but I felt strong effects. However, I gave much MDMA to my body because of my tolerance, and I know that my tolerance is so high that I could take more than 0.6 without being too much high but your tolerance doesn't change how bad MDMA is for your body so avoid to go over the amount of 0.4/0.5 even if you have a high tolerance like me (set a limit as i said).
The particularity of MDMA is that everytime you take MDMA, you tolerance becomes higher. I'm not talking about the tolerance due to the lack of serotonin, this tolerance disappear in the next weeks (during a session of MDMA, you empty your reserves of serotonin and you need to wait at least 4 weeks to recover a good amount of serotonin while the serotonin is important for the effects, so when you take MDMA it is better to have serotonin in your body to maximize the effects, that's one of the reason why it is stupid to take MDMA every week), I'm talking about the tolerance which never disappear and which becomes higher after every session. This tolerance is why your first session is unique and why you have to take more MDMA every time to feel usual effects.
Anyway, if you are in my case, I don't advise you to take more than 0.5, but if you need more to feel strong effects or if you want very strong effects as hallucinations (if you have very strong effects it means that you have to be very careful) I advise you to keep an eye on your physical state during the session.