I also have this combination, I use it with the 1.6 crop facter cameras to get real telephoto performance (you can crop the FF format to get the same telephoto power at the expence of loosing pixel density resulting in a smeller image). I can see no loss in sharpness when combined with the 1.4 TC, If you do get the 2x TC, try focusing with the 1.4 TC in place using AF, after this is done, replace the 1.4 TC with the 2x TC (be careful not to moove the focus in doing so)

I love this lens and I keep the ISO at 400 plus to ensure a good shutter speed

As was said before f8 is a good place to start to get a bit of DOF

This lens can be used handheld but is best on a tripod and gimbal
I have the Manfrotto 055MFV and Manfrotto 393 head

All I would say is practice, practice, practice... I am and I am already seeing some good images from the lens... (only had the lens 3 weeks)

The 1.4 works very well with this lens :)

Can we see some shot from this bunch of glasses here?

here are a few of mine from earlier this year, all taken with the 500 f4 IS, 1.4x tc and a 40D.