Using an iMac as a display for PC laptop in dual mointor configuration
The iMac will connect to a Thunderbolt port. (But no other.) Also, you can't 'daisy-chain' the iMac in Target Display mode to another monitor. 

And the TB Display also can't be daisy-chained, but it can connect to other video ports. So you'll need to use another video out port on the Lenovo, with all the necessary adaptors to get it to the TB's connector.