Bulbs isn't actually a legal requirement, I don't think - though you can be nicked if you have a bulb out on your car (which is why people carry spares).
Best advice - route through Luxembourg if you can. Petrol there is a lot cheaper than anywhere else. In France in particular, go to supermarkets for petrol. They're much cheaper. Germany is pretty expensive all over for fuel. The Netherlands is even worse.
As for the car, check your cooling system. Any signs of weakness in the radiator, change it our before you go. Check all the usual stuff - suspension components, driveshafts, condition of tyres. Much easier to fix before you go than try and haggle with some German garage!
Note that they drive on the wrong side of the road once you get off the ferry. You get used to it in about 5 minutes, once you've got past the first roundabout and figured out which way to go round it. Just follow what everyone else is doing.
It's a good idea to keep your headlights on when out of built-up areas - this is a legal requirement in some countries, and a good idea anyway.
Insurance - check your policy. Most Fully Comp ones will cover you in EU countries to a minimum standard (3rd Party) so you don't need to buy additional cover unless you want Fully Comp cover abroad. If you're only insured 3rd Party here, you may have to buy additional cover for the period abroad.
Some countries require purchase of a sticker for using their motorways (e.g. Austria, Switz, Hungary, Czech), but not Germany (where they have loads of roadworks) or Belgium. French toll roads ("Peage") are quite expensive, but you may manage to avoid all charges if heading to Poland.
Take a bit of a toolkit with you - spanners/sockets in the usual sizes, screwdrivers, pair of pliers and some cable ties and a roll of gaffa tape. These can prove invaluable!
Angus