I feel for you, and in fact i had EXACTLY the same experience my first time, in fact, it was so intense that i was hospitalised.
I won't go too much into detail, but i basically started to panic when i felt the drug's effects coming on. I was heating up badly, and my heart was racing (i knew these would both happen, but i was thinking about it so much that i was really freaking out.
I tried splashing water but it wasn't working (bear in mind i only did this one time

), and to make matters worse i was already very drunk. This added to dehydration. As you said, i began to feel extremely weightless, as if my arms and legs weighed nothing, and i was having tingling sensations all over. I've never been so scared in my life. Eventually, my friend took me out, and literally got me to hospital JUST in time, which i am still very thankful for. I spent the next night on the drip, feeling like an ass (but a very happy/high one

).
I felt side-effects for a few weeks after this incident. Namely that my heart would feel fast, i wouldn't be able to breathe calmly and properly, and my mind would just feel like it was "zapping". It's very hard to explain, but it would feel as if something inside my head was floating out, but when i concentrated on it, it would simply just shoot back in. I felt scattered, unfocused and couldn't do exercise without feeling really messed up. I also vowed never to take ecstasy again.
However, if nothing else, my curiosity and determination to prove that the drug was safe and i was just careless (i had double dropped on my first time, very strong pills) i did extensive reading on the drug for about a month. It took me about a month and a half to return to normal after the hospital, but eventually i had read enough about it, came on Bluelight and asked some questions about it, and just realised that i was not ready to experience what i did, and certainly not at that strength.
It must be noted that i had a severe panic attack when i smoked weed. This was a few weeks after the incident, and i had only smoked weed about 3 times previously, and i smoked a HELL of a lot. This lead me to think about my heart beating faster (I didn't realise at the time that weed did this) and thus resulted in me thinking that it was kicking the Ecstasy back so to speak (silly i know). I had to go to begalaas' house and sleep, and that wore off.
So anyway, i was bored one night, and me and a friend decided to go to the nightclub that i had the problem at. It is known to be a dodgy place, but i enjoyed the music and the scene, and he wanted to try Ecstasy, and i thought "well i can go along with him, i won't try it but i will watch over him, after all, i came through trouble!". So anyway we head off and get there, and he drops half. Feels nothing after 30 mins and decides to drop the other half. After a while he starts to feel very happy and high, and it gets stronger and stronger in a matter on minutes. And then i saw how much fun he was having (i never had that), so i decided to bite the bullet and drop. I said i was going to the toilet, bought a pill and dropped it. After it kicked in, i had the time of my life. It wasn't a strong pill, and i was nervous before i took it, but the minute that it kicked in i knew how sad it was to be so scared. I was so happy, i danced the night away and had overcome my fear.
So what caused me to overcome it? I had read up on it, knew what to expect, took it easy, took regular breaks, drank enough water but not too much, and just thought that if it gets too much we can leave. There isn't much to it, and therefore i believe that at the end of the day you just need to be careful, and take less than you think you may need. If your friends take one, take half. It's better to not feel too much, believe me! You can always take more after. So yes, my advice is to split the dosing. Take half, then a while later take another half for example.
I can't help you with the whole benzos thing, as i have never taken them (haven't needed to). But other things you could do are have a sober friend there, be in a quiet environment (the club we go to is very hostile, dark, noisy and has techno music, not good for a panic attack trust me!) and just remember that if you have good pills, Ecstasy can be one of the safer drugs. You have done it before and enjoy it. Now i have no fears and do it often, and everytime is as good as the last. Just be careful. Happy Rolling.
Peace
Rich