We met with our caterer/venue and it turns out they do have high tables we can use for our cocktail reception. (Originally we had thought they only had low tables). As the ceremony is in the same room, we need 100 chairs for all guests for the ceremony. However, for our cocktail reception immediately afterwards, the possibilities are:
Half (5) high tables with no seating, half (5) low tables with seats (enough seating for 50 of approx. 100 guests)
OR
Half high tables with no seating, half low tables with seats and extra chairs around the perimeter of the rooms, so everyone has a seat (all 100 chairs)
OR
The above choice, but only a handful of extra chairs, so not everyone has a seat, but chances are not everyone will be seating at the same time. (75 chairs)
OR
Stick with all low tables (which was our original plan) (100 chairs)
OR
Ask people to sit on the floor (no chairs!) 