To answer your first question, as received from the factory my v6 uBitx is drawing 730ma for the test when I press the mic PTT button and do not supply any sound to it. I have not changed the bias, so assuming all was set as per the instructions, then my starting current would be 530ma, just 10ma below what you are measuring. That is supplying 12.0 volts, not 13+ volts that most amateur power supplies provide. It may be that the tuneup guide has not been updated for the larger display that draws more current.
To answer your second question, No, what you have done is not reasonable. You still want to increase the bias to draw 100ma for each of the IRF510s. That means if you start with the 540ma then the total should be 740ma when the two are adjusted correctly. The reason is that you want the IRF510s in their linear region, which starts at 100ma (give or take a few).
Above are just ideas and measurements that I did on my uBitx. Raj was involved in the development of the uBitx so may have more information.