if you want to run without a filter, that is fine, there a ways to do that. however, running without any electrical equipment is not going to work.
without a sump, you will need:
1.5 to 2 pounds per gallon of live rock. the amount of space this rock will take up in your tank will depend on the type of rock you buy.
a skimmer.... yes, you will need a skimmer, unless you are willing to do daily water changes to remove proteins from the water.
powerheads... you will need water movement in the tank to simulate the ocean's currents, and to prevent algea and cyano
from building up on your rocks. try to aim for 10 times your tank volume as an hourly turnover rate. i.e. a 75 gallon tank should have 750 gallons per hour water movement.
if you go with a sump, you can ditch the powerheads and use your return pump for water circulation. make sure that you look at the flowrate vs head curve to determine if you have adequate flowrate once the water gets up to the tank. another thing you can do if you have a sump is section off part of it as a refugium. you can use macro algea in there to remove some nutrients from the water.
be advised, if you do add live rock to the tank, it may induce a small cycle due to die-off from the live rock. i would not add any livestock to your tank until you decide what you are going to do for filtration. also, how much sand do you have in your tank? are you planning for a deep sand bed?