Do a search for 'Easy Flange'. You can order the tri-clamp from Mile-Hi, Brewhaus, St. Pat's or McMaster-Carr. I also recomend the PTFE gasket. You will need to remove the ridge from both sides of the gasket for the keg to Easy flange connection.
A thumper is a nice accessory, but not needed at first. Yes, the vapor is what heats the thumper.
Build the still with a union fitting between the lyne arm and condenser, then you can add/remove a thumper in the future.
It is the very things that we think we know, that keep us from learning what we should know.
Valved Reflux, 3"x54" Bok 'mini', 2 liebig based pots and the 'Blockhead' 60K btu propane heat