Olympus camera with Panasonic lens

I'm planning to buy a Olympus OM-D E-M5  and the following Panasonic lenses:

1. 12-35mm f/2.8
2. 35-100mm f/2.8
3. 100-300mm f/4-5.6

I know that Panasonic lenses are compatible with Olympus cameras, but are there disadvantages in using them?

Can I expect the same focusing speeds ?  What about moving objects ?

Which IS should I use ?  Camera or lens ?

Thanks for your help

J

Jules Gobeil

Nature photographer - Photographe de la nature

www.julesgobeil.com