Shaking hands when greeting

Assalamu alaikum,
Respected Mufti Sahab, I want to know if shaking hands with one hand is sunnat or shaking hands with both the hands is Sunnat. I have heard that shaking with one hand and with both hands, both is sunnat. So, if this is the case then while following any one sunnat one will get the sawab.

2. Aslo after shaking hands people place there hands on the chest is this a sunnat also or one can just shake hands and thats ok to follow sunnat.

Jazzak Allah!