One of the best things you can do is to drill a 4mm hole in your stat, as this helps eliminate air locks when refilling.
Having just done my sapphy I would say they hold somewhere around 7/8 litres.
I wouldn't worry too much about operating temps especially if new stat, as old one may have been lazy, just let it get up to temp so fan cuts in, then leave overnight to cool down, it will draw out any air, make sure you leave the cap on all the time it is running, as there is no reason it need be off, and it needs to be there to help develope a vacuum that draws air out upon cooling.
tabetha