I agree with the person in Germany who said you are missing the point a little if you're eating Dinty Moore from the can in Europe. I have just finished a tour in Spain and Portugal, and as an "old" guy (70, going on 71), I'd say the following:
1. 30-40 miles a day won't even get a young guy like you fit.
2. I usually ride from about 8:30 am to about 7:00 pm (depending on local sunrise and sunset). A lot of that time is spent in cathedrals, ruins, museums, etc.
3. I find 50-60 miles a day an easy rate for Europe (80-120 miles a day in USA or other countries with long distances).
4. Can't speak to bike or tires: I own a Bianchi tourer, but have used a rented Brompton for the western isles of Scotland (you don't have to pay for it on ferries, and fewer potential problems on trains), as well as a ridiculously over-prepared rented mountain bike in Andalusia and a rented "fished from the canal" bike for Eu19/week in northern Germany. Had no problems with any of them.
5. My tent is an REI "1.5-man" tent - wide enough that I can get all my panniers and me in it. However, this American tent is less than perfect for Europe because it has traditional guylines, which people in crowded campgrounds trip over, and the flysheet doesn't reach the ground, which is disastrous in a N. Atlantic storm.
6. In Spain and southern France, in the height of the season, campgrounds were Eu 10-12 per night.
7. I carried a stove/cookware and didn't use it. My food budget was: Continental breakfast Eu 2-3.00 (at a bar). Lunch: Eu 8-12 for a real restaurant meal. Dinner: Eu 6-10 for a BIG snack (occasionally Burger King, but here again that is defeating the purpose). I also spent about Eu 1-2 per day for fluids - I carried 2 standard bike bottles on the bike, plus one 1 or 1.5 litre bottle in a holder and another one bungeed on top of my tent on the rear rack. Total Eu 18-25 for food.
8. I rarely bought pastries, etc., because I have a gluten problem, but that would have lowered costs by about Eu 5.
9. Don't underestimate how much fluid or energy you will use: on hot days I would find myself draining a 1.5 litre bottle of lemonade at one go when I stopped riding.
10. I rarely locked up my bike in campgrounds, but was religious about doing so everywhere else. I have toured all over Iberia, UK, N. Germany and never had anything stolen at a campground or hostel: once that starts to happen the whole system of student/low budget family travel will break down.
11. If you have a problem fitting panniers, as I did with one folder, you may be able to attach a rucksack between the seat post and a light rear rack, using enough bungees. This also has the advantage that you can take off on a 2-day hike if you feel like it.
12. That reminded me: pedals and shoes. I tour in old running shoes, which also gives me the flexibility to hike. I met a Scottish girl who was touring in Nova Scotia wearing heavy flip-flops in pouring cold rain. Her reasoning: when it stops your feet dry off rapidly. I never use bike shoes or pedals with clips.
13: Panniers: the best ones I have are Axioms, a Canadian foldover brand. I always wrap everything in plastic bags inside the panniers - an accident can be costly - my Passport almost dissolved after riding through the edges of a hurricane in Louisiana, and I had a pannier full of mocha Coffee to boot.
14: I have broken 2 chains and many spokes (I weigh 220 lbs/100 kg). However, since getting a new rear wheel with higher-quality spokes in Whitehorse, Yukon, to replace one whose rim wore away in a storm on the Top of World Highway, I have never had a broken spoke again. So if you are big and have a low-end bike, I think rebuilding the rear wheel with high-end spokes may solve any problem there.

Good luck in France: I'll be there myself in July, riding from Aquitaine up the west coast and around Brittany and Normandy to the UK.

JohnB