Congratulations on your purchase. Nice low miles.
I drive the same 2004 545i beast and it is a monster!
Do not be lulled into complacency with your low miles, however. Many items such as the plastic components of the coolant system deteriorate based on age rather than pure miles, so keep an eye on the cooling system.
You may or may not have received maintenance records with the car. If the BMW condition based maintenance was followed your oil may have been change only two times in the car's life. An ideal situation would have been twice per year or 16-17 times so far. You can't do anything to reverse the past, but you can start fresh now.
If you have no record of a recent oil change, change your oil immediately. Then change your oil every 5-6K miles, 250 operating hours or twice per year, whichever is less. This is by far the most important thing you can do to maintain the health of gaskets and seals, which experience has shown is an acknowledged weakness in the 545i engine (N62B44).
I suggest you choose an oil from the BMW approved LL-01 list of oils. I use Mobil 1 0W-40 because it is widely available at retail and has good high heat, high shear characteristics for a relatively light 40 weight oil, however there are many good oils available. If you change your oil every 5K miles you will maintain a relatively high level of additives, minimize oil oxidation and keep the oil very alkaline, which is easy on gaskets and engine components.
Post up if you would like additional information specific to the 545i or E60 in general.