Okay, about the muscle spasms, that's just a normal response when you touch them.
The previous owner of this snake was a horrible owner and did not deserve that snake.
As for feeding, I typically go with either 1 rat or two mice a week, though I'd wait more than 5 minutes to offer the second.
Please please do not feed him a live rat, if you decide to go for rats go with frozen. I've seen too many snakes that have been injured by rats.
Studies have proven that you do not need to feed him in a separate container.
Give him a lot of time alone, he has to adjust to you.
Also, your thermometer is not one of those crappy gauges like these are they?
these are incredibly inaccurate, go with a digital probe.
Since your screen top does not lock, make sure that he cannot lift it up, my first bp could open it with his head.
The most important heat is belly heat, so a lamp isn't necessary and wastes electricity, but if you like it or cannot keep the temps up, it's perfectly fine. I'd go with some flexwatt heat tape because you have such a large aquarium.