IME there’s no need for verbal communication, and signals don’t need to be over the top, just subtle movements are all that’s needed.
I’ve also never needed to compensate for obstacles, if your on the wheel just follow it. If your half wheeling you’ll see what’s coming anyway. Drafting through towns and cities on open roads is dim anyway.
Though I’m just a nobody I’ve been fortunate to ride with pros, ex pros and future pros from the UK France and the States, and none of them say a word. It’s actually a very simple proccess following a wheel, and bear in mind I’m technically inept off road.
And like it’s been said up there, when you come to the front you should just arrive there. When I’ve been out with newer and fit riders they nearly always get out of the saddle and pass in a way that’s more akin to an attack.
As for being easy it’s about 30%? but drafting doesn’t always mean sitting right behind someone, you can experiment by moving side to side and overlapping wheels.
As for distance I’d keep it to a minimum of about 50mm for now.
I’d get learned up first though if possible.