Trailstar frame. Fantastic condition for age, one of the first made. £45. You will find cheaper on ebay but I don't think you'll find one this old in better condition. The pictures speak for themselves...
I don't I'm afraid. I only have ever run single speed. I could supply chain tugs for chain tension but not to run gears. I should imagine they would be still quite easily availible
No rust. I'm not 100% sure of the seat post size but I can find out tomorrow for you. Well I didn't really want to swap but post a picture of the Viper frame and we'll see if it temps me.... (Always looking for a new build! )