Outside!

I've had my dog for two days now...she is a Chihuahua...she is 8 1/2 weeks old and has had not vaccinations left...I just wanted to know when should I start bringing it outside for training? Would it be a good idea to walk it around the backyard since it has no needles yet...and lastly is it too young for the leash...how old should it be until I start using a leash(it's actually a body harness because they say Chihuahuas have fragile necks so you can't really use a leash around the neck)...I'm also scared that since hse hasen't had any vacinations yet, she might get sick from going outside...any comments would help...

Thanks