@arpie and @kmakm have covered pretty much everything. My family including the kids, knew from the start, as did my manager at work. You haven't said what surgery you're having, but you may want to wait until your path report to discuss the situation with your new workplace if the timeframe is going to allow it. As far as telling friends and colleagues, I told a couple of key close friends and asked them to tell others and keep them updated. Then I started a blog, gave the details out and keep people updated that way.
As well as taking someone with you to appointments, you may want to jot down questions as you think of them so you don't forget.
It is perfectly normal to feel overwhelmed. Take things one step at a time, let those close to you support you and try not to put too much pressure on yourself. And come back here when you need to rage, ask for info and support, or need a bit of a laugh.