The d40-80 are all older models (I have the D60)...The D90 is an upgrade that includes HD Video option...

Here's the problem I see with your issue. You want to turn this from hobby to profession. You really need to move from DX to FX sensor to do this effectively...and that means $$$.

Pretty sure anything in the line will work, lenswise...but the 7000 is probably your best upgrade path...you will get higher res and much better light handling. That's the biggest issue I have with the 60...it sucks with low light.