It fielded three infantry Divisions of around 7000 men each, plus the Indian brigade which consisted of +/- 3500 men. The cavalry consisted of 7 regiments spread in three brigades, 3200 men in total. The artillery consisted of 8 batteries of 6 six cannons and two howitsers manned by about a hundred men.
In total that's over 30.000-33.000 men. That's only counting those who would fight in the campaign and march into France - There were plenty of units who stayed in Belgium, which would make the number near 40.000. Of course, this is also not counting the depots, garrison companies, swiss troops, the colonial hussars (1 sqd), the militia carabiniers (full regiment) and the 30+ batallions of Militia still in training.
Like I said, the quatering only happened during the months prior to the battles - the units were split up, sometimes to a single company in a town, to fit them all in, as well as guarding the border.
It was ordered that 15-20 men had to sleep in one house at least, and after a fake alarm that did not give satisfying results, it was forbidden to be quatered more then 1500 steps from the town centre.
It was also forbidden to be cooked for by the citizens you were staying.
