how long to wait before pitching?

You really should plan for your starter to be ready to pitch when the wort is ready for it. Having said that, you could speed up the settling (assuming the starter is done) by cold crashing the starter in your fridge, then decanting and pitching. Some will tell you not to pitch cold yeast into wort, but it's a fairly wide (though not the most common) practice and seems to work fine. Some of my best beers have been 'cold pitched.' Or you could just pitch the whole starter (no need to wait and decant), but you may not want to do that if it's very large. (Personally I always decant.)

 

I would probably pitch ASAP, to be honest. Waiting for the starter to settle is going to take something like 8 hours I would guess (I usually leave it in the fridge overnight) and I probably wouldn't want to leave the wort sitting for that long. Chances are it'd be OK if you were very careful about sanitation, but it seems to me a risk not worth taking for the sake of avoiding the necessity of adding 1 liter of starter wort. Also, I think you should aerate immediately prior to pitching--leaving it sit will allow the wort to degas somewhat.

 

I don't think waiting is such a big deal. I can cool wort to 65 or so very rapidly, but if I'm making a lager, I don't pitch until my cooler brings the wort down to 48 or so, which generally means letting the wort sit in the cooler overnight. I guess you could argue that at cooler temps, the risk that an infection will take hold is minimal. You said you were confident in your sanitation, so I say, RDWHAHB.