As others have said I'd start with a thin pick since you're in a bit of a tight spot.
It'll bend more as you hit the string so you won't have to grip it as tightly and you'll have less chance of dropping it because of this.
As for playing position it's whatever feels most comfortable for you. I play with my bass low so my right arm pretty much straight, otherwise my elbow aches if it's any higher. But that's just me.
However, since you're in a rush, is suggest leaving your strap at whatever length you usually have it. If you lower it it will also change your left hand positioning which can be difficult, uncomfortable or even painful if you're not used to it.