to get past 18 (5-2) simply kill yourself on the spikes, all the way to the left and push the cart along, you may have to jump when the wheels hit the gap
When you start to get your hotel higher up, one thing that you need to do is not build an elevator all the way up, have 2 next to each other, altering which side it is on every 10-15 levels and the elevator will spend more time dropping of guests than going up and down