Before even that, have you checked the floor structure to verify it is strong enough for tile? It's often easier to tile the floor then the walls because you don't have to be as neat with the tile cuts at the walls - the wall tile will cover those. Note, do not tile to the wall, leave a (small) gap and do NOT grout it. The tile needs some room to expand. If you want to avoid caulk at the joint there, www.schluter.com makes some expansion joints designed for wall/floor transitions. Then, it doesn't matter which goes first, since each edge needs to be visible.
If the floor is not adequate for tile, do you even want to walk into the room? The weight of the tile is evenly distributed over the entire area, but YOUR weight is concentrated at your two feet.
The problem is not the weight of the tile, but the fact that tile doesn't like movement. If the floor is not solid enough, the deflection will cause the tile/grout to crack.
I agree that the OP should check out johnbridge.com (lots of good info on the subject and very helpful people).