Take it easy, make sure it's got correctly sized, decent branded tyres on it and you'll be fine just show it uber-respect especially in the wet, and don't give into the temptation to mess about with it to "see what it can do".
I was in your boat, the supra is my first RWD car, and to be honest even though I was careful with it, I nearly crashed within a week (wet road, one second of stupidity trying to 'race' a Porker and it slithered like a snake ).
There's no electronic overlord or 4WD to help you out of a tight spot, but that's what makes it so rewarding .
Oh and one more thing....I eventually picked an auto because I wanted to keep both hands on the wheel when nailing it Turned out to be a good decision!