200-250 Miles a day is about right if avoiding the motorways. You'll probably average 40-50 mph when taking account of stops etc, equating to 5 or 6 hours riding. Gives you plenty of room for minor issues.
On my last European bike trip, one of the riders didn't have bike recovery insurance as the bike was over 15 years old and no company would insure her. Unfortunately, in the south of France, the bike in front of her hit a patch of diesel and went over, she collided with the back of it and twisted the front forks making it not rideable. She had to leave it in a local garage and pillioned back home. My advice would be to make sure, where you can, that you take out recovery insurance.
I have done independent trips to the continent for the last 4 years, and found Spain to offer the best roads and cheapest accommodation. So easy to do it yourself. Just be aware, sometimes the addresses for accommodation are not good lol.
For ease of access and cheap is France with little or no traffic is worth considering. Problem is with "the best roads" comments is down to folks opinion and depending on what you like to do yourself :) . I've run many euro BM trips over the years and so much to choose on doorstep.
http://www.bestbikingroads.com/ is good start for routes then you can tweak to suit
http://www.fema-online.eu/website/index.php/consumer-information/riding-abroad/ actual laws by country
If i can help with anything post here or send me a pm as i work with touring groups
After touring Central/Western Spain last year, and keeping off the motorways, I saw very few fuel stations. In many parts they are few and far between so a small capacity fuel tank could cause problems. Regarding hearing stories of billiard table like roads, yes they are in general superb, but, when taking some of the minor roads, I encountered a few that were a lot worse than I've ever ridden in the UK. I personally found that using the A/B road equivalents, 200-250 miles a day is as much as I wanted to cover.