The 'trading' thing is definitely one to steer clear of! Day traders are just mugs, frankly - if you could actually make money from it, we'd all be at it. It's glorified gambling.
It's a tricky one, this. On the one hand, I perfectly understand your need to earn a crust, particularly if you have already financial commitments from before you became a student. But really the studying has to take a great priority over earning. I understand that you don't want to go back to building work, even on a casual basis - would you consider working as an odd job/handyman? There's an awful lot of people who are too busy/inept to put up shelves, fit doors, mend cupboards as the like? You would get to choose your own hours, set your own pay rate and be your own boss.
Just an idea.