I think it would be cheaper to just buy some panaracer presela tyres for your MTB wheels.
What wheel size is your bike built with? 26"? you can't use 700c with that.
If you want to stick with the idea of a 700c wheeled FG bike, you'd probably want to go with an entirely new bike built like that.

Otherwise...
just get some slick/light tread tyres for your wheels
You can lock out the suspension on the fork to make it solid.
maybe add fenders...