As you are seeing just in this short time, marine tanks have as many options as there are hobbiests
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My personal preference is more in line with Corpusse. LOTS of GOOD live rock, IN the main tank, as large a sump as you can manage and simple filtration (I use a filter sock at the overflow with a bag of charcoal (not as much forced flow through as a canister but not passive). I rinse the charcoal weekly and exchange it about once a month (I actually keep two bags filled for each tank and swap them weekly so for maintenance I only renew it every two months).
I HIGHLY recommend you reduce your sand to half. Sand beds tend to be major collectors of pollutants, are hard to clean and give little surface area for positive bacteria. I disrupt mine vigorously weekly and vacuum as much of the waste "dust" as I can during the water exchange process. I don't put sand under or behind my LR (it gets there, of course, but I intentionally don't put it there when setting up a tank) and my octos have removed it when they den on the tank floor. Unless you set up a DSB (6" or better of undisrupted sand that is over 1 year old and I really have not seen benefit until 2 years) a sand bed is a nitrate producer and waste collector. If you want to create a DSB for an octo tank, that is best done in the sump or a separately connected tank.
Keep in mind that your sump needs to accommodate the amount of water that will drain back into it when the pump is off. So a 20 gallon sump will only contain 10-15 gallons of water (toward the lower end after LR and equipment displacement). I have found sizing them to roughly half your water volume is about right (again you will not have 1/3 your water volume actually in the sump but it seems to be a good go by for sizing). If you can manage a 30 gallon tank (talls have narrower foot print but height is a problem with tall tanks though because of the skimmer requirements if you are putting it under the tank) I would recommend it as a minimum consideration. I still have a couple of tanks with undersized sumps but have enlarged others as time, money and space have permitted.
There is a long forum post on skimmers that is "stuck" to the top of the Tank Talk forum that you may want to read if you have not purchased a skimmer. It may help you find units to avoid more than specific recommendations for your budget.
If you are having your tank drilled (i.e. if it is not already reef ready) lowering the bulk head to allow 1.5 to 2" of air space above the water line is very helpful in dissuading escapes. I also recommend a 1.5" - 2" fixed lip around the circumference of the top for the same purpose.