Fiber -- singleMode to multiMode ?

I have three buildings about 1,000 feet from each other.
 
My ISP #2 is able to get into building #3 for $15,000
less since they don't have to bore under a parking lot/etc
 ============================================================
1. can I do the below between buildings
    since I have SPARE fiber already terminated
            OR
    do I need to go into each building's SWITCH,
    not just the PATCH PANEL ?

2. is the below #1 doable
            OR
    do I need something like
    http://www.huihongfiber.com/single-mode-multimode-converter.html
    not just the PATCH PANEL ?
============================================================
1. Building #3
       ** ISP #2 comes in at this building
       ** SC "single mode FIBER" end into
            PATCH PANEL's unused internal
            "multi-mode FIBER"
       ** feeds into Building #2 PATCH PANEL

2. Building #2
       ** FIBER into Building #2 PATCH PANEL
          from Building #3 PATCH PANEL
       ** FIBER out of Building #2 PATCH PANEL
          to Building #1 PATCH PANEL
 
3. Building #1
       ** FIBER out of Building #1 PATCH PANEL
          to Building #1 firewall as ISP #2