Yes, right clicking is fine. It will still open the window using the tracking URL Google generates for the advertiser.
I have an Adsense tracker that tracks all of my impressions and clicks (as well as referrer, ad size, colors used, advertisers link, and more). I've noticed my CTR as high as 300% sometimes. How? Basically, a visitor will come to one of my sites (1 impression), click on an ad, then come back and click again (2 clicks). Whether they open a new window or just hit the back button, I don't know, but I haven't seen more than 3 clicks per IP. Maybe Google has a limit (or security) on how many ads a user can click on.
yeap, it couts as "clicking directly". So if you do it on your own site it will be seen by google as invalid clicks. All the code that gives you money for the clicks and that can get you banned for invalid clicks is in the URL which is also used in "right clicking" . Only thing you can do is either copy the url and cut the advertiser's url itself from it, or get the ad preview tool.