On a D7000, the far end of the 18-200 will get you 300mm equivalent reach.
On the GF3, the 14-42 will reach 84mm equivalent at most. You need the 14-140 to get close. But when you fixed that lens on your GF3, the whole thing is not that small or light anymore. Worse, the ergonomics always feels "off balance" to me - esp. with my need for reading glasses... operating it without a EVF is a challenge.
If you get the GF3, and need up to 300mm FL (FF Eq), its best to pair it with the 45-175mm Panasonic X lens (90-350mm FF eq). Small and light. Slightly over 200g for the lens.
Theres a review on this lens in the review section. You prob will not want to pair this with the 14-140 as that is a superzoom lens thats a little more heavy (440g).