Here is my biggest piece of advice when it comes to UGFs, and I have lots of experience with them...get thee a serious powerhead. In fact, for a 75 gallon tank (assuming the UGF system has two plates), get thee TWO serious powerheads. (I just bought a replacement powerhead for my 75 gallon from Fosters and Smith for 25 bucks...295 gallons per hour. This will go along with another of the same size.)
Running a UGF with air is a collossal joke, and it will do you harm in the long run. Live plants rooted in the substrate are generally a bad idea. The roots will clog the plates. Do not use sand. Get a gravel that is around 3/8 to 1/4 inch in size, and put in 2-3 inches of depth, max.
And yes, use a gravel cleaning syphon the right way, and clean 1/2 the tank on each water change. By "right" I mean go straight down (all the way) into the gravel with the open end and hold it there for a few seconds, until the water runs clear and all the crud in that spot has gone up the tube. Lift straight up and move over to the next spot and go straight down into the gravel...repeat. My apologies if these directions seem overly specific. I spent some time on YouTube yesterday trying to learn something new, and was dismayed to see several instructional videos on how to clean aquarium gravel that were so WRONG (and stupid) that I was bug-eyed with amazement.