Somewhere in this forum I posted detailed instructions for installing Juno mini-track lighting. It should be just the same as the Seagull lighting, the only difference is the Juno uses a track and Seagull I think uses a wire.

You might want to try a search on here for Juno Trac 12

I think your electrician is wrong.
I would specify double the number of lamps for 17 feet.
Perhaps you should have the electrician install a more expensive 250 watt transformer, and if he's wrong you can add add more lamps.
I use 15-20 watts per foot for my indirect valence applicationsand I think you would require at least that level of output.