I've done several bike trips to Europe. There's already some good advice here, but to add a fee comments...
Don't dismiss Belgium - the WW1 cemeteries such as Tyne Cot are well worth a visit, and don't require any interest in military history to be genuinely moving. Same for the Menin Gate at Ypres, although you may have done these at school.
When travelling in France there aren't really many travel lodge type places by the side of the road, so you generally need to reach cities. We usually alternate, and do a few nights in a formula 1 which are ridiculously cheap no frills accommodation at 30 euros per room including breakfast, and then have a few nights in somewhere much nicer. You can always find somewhere to stay though - we never book anywhere in advance as that just puts pressure on to get to places. If you're in smaller towns, park up and head for tourist information, as they will ring round the local hotels and b&bs for you. The only time this nearly failed was when we ended up in Ypres to find the Belgium rally was there, but even then Tourist Information managed to find the only remaining room in town! I quite
I've bed and breakfasts as you come across some real characters.
Food - we're lucky that we both enjoy any food at all, so we generally play lucky dip, and just find a restaurant and point at random food. It's a good way of trying new things

. Food is generally cheaper and better quality than the equivalent in the UK, however in Germany it was very mixed, but we did find an awesome little restaurant at the end of the D500. If you're in a big tourist city like Rome, just move away into the back streets and you get better food at half the price.
Spain - the main roads are stunningly good quality, but the roadside motels often double as strip joints and brothels for truckers!
Right, got to go to work, but will add more stuff later