For quick network diagrams we use Nectus   www.nectus5.com it can do topology auto-generation after Discovery is complete  

to poll for Interface utilization you need to read byte counters first time at moment "t" and then second time at "t+n" and then calculate difference and divide it by "n"..  this will give you throughput in "Bytes per second".. then you take interfac...

Nectus or Solarwinds can be used to push specific command scripts to devices at predefined time