That also saves the rest of us time to respond to "fresher" questions, such as your short-range move. Others have their own more legitimate excuses, less whiney than mine, for not responding immediately. ;)

We have moved three times, over short distances, in much the manner you describe. The first time there were 15 fish tanks and 25 boxes of books and a smattering of furniture. (Except for the aquariums, that is probably typical of grad students.) The next couple of times those things increased in number and weight. The number of friends available to help with these treks seemed to decline with each move. ;)

That 55-gallon tank would be tricky. I think New Guppy Mamma's suggestions of bringing some water in buckets and the gravel in buckets are great ideas. I can only imagine the hassle of moving fish 2,000 miles!

If you get two colors of buckets (maybe on sale from your hardware store) rinse them out ahead of time. (I bleach and dechlorinate them but that may be overkill.)  You will find uses for them later as "out" buckets and "in" buckets for seasoning and delivering tank water. If that gravel and water is placed in the 55 not long after you have leveled the stand (got a cheap level used for hanging pictures?) and the tank, that stuff should be mostly ok. Throw at least an airstone in the tank as soon as convenient. Larger tanks must be level and that may involve some "shimming" where paper or cardboard is put under gaps on the stand. The tank should be as level as possible and not sway at all on the stand when empty.

Moving large aquariums such as the 55 with much in them can be dangerous so they should be empty. (Sigh.) I recommend using leather garden gloves to carry the tank, if you have them around, so the aquarium doesn't slide and so you or a friend don't get nicked by glass edges.

If you use box or sponge filters or a powerhead with a sponge on it, it/they can be placed in the 55 to keep the show moving. A submersible heater (my non-scientific prejudice favors them as more flexible and durable) will keep conditions more comfortable and you may be able to return/ introduce your guppies to it fairly smoothly. Just feed them very lightly, the second day on for a few days.

HOB power filters are a little trickier. Except for them, I would be quick to point out that there is no law, which says an aquarium must be full. (Indeed I have a couple with fish renowned for their ability to leap, and complete tops and floating plants not-withstanding, water levels in those tanks are several inches below the top. (Small permanent marker marks on the back of a side will betray the highest I dare take the water.) Swordtails are likely candidates for lower  water levels.

If your fry will avoid power filters, you might be able to put it/them in there until the 55 is full.

You will be taking down your 20 with the fry. Put the fry and a lot of their water in buckets. (Or a safer approach would be to bag the fry and put them in a styro.) If you can put the stand in the trunk and the tank in the back seat, carefully distributing the buckets 'round and about, you probably could make a specific run over to your new home and set those guys up. I did something very similar in moving a couple tanks to college (grad school), a mere hour from my folk's place, later back home and then yet later another hour down the interstate to my apartment near where I started teaching. On that last run, somehow I packed a lot of water, fish and glass into a Volkswagen bug and then avoided a low-speed head-on by the cars ahead of me without actually dumping anything off of the seats, while careening down ths shoulder around the suddenly introduced vehicles in the middle of the road.

(I was worried about clinking jars. Later it occurred to me that being concerned about a crash and bleeding to death from glass shards might also be relevant.)

When married and accumulating entirely too much fish stuff, we moved 2.5s, 5.5s, 10s and even 15 and 20-gallon tanks from nearby suburb to nearby suburb with a little water and the smaller fish in them. We did get away with dropping the water to about an inch level and sliding them into an already warmed up van or station wagon. The tanks were often modestly populated and some seasoned water was waiting for them. Since the room we were putting them in had its own heat source, we could keep them somewhat shallow and not worry too much about heat. Temperatures were near the lower part of their comfortable ranges. The second day here the 60-70 "tanks" were recipients of another inch of water, if they were already on the more or less leveled stands they would be permanently staying upon.

The lawyer for the sellers of our house, stalled our move a couple of weeks until early November, right about this time of the month. While it can be very cold in Illinois, come November, we were lucky then to have the mercury creep into the 60s F, as it is this week. The vehicles conveying the tanks kept the fish from chilling too badly. I was lucky to have been able to especially do frequent water changes and feed them well the couple weeks before the move. So the aquariums were relatively clean and the fish pretty fat and healthy and they hung in there well.

You have a bit of an advantage with your climate, but I'm sure that Georgia gets pretty cold, probably just when you want to move. I hope you have more time than we seem to have. Our moves seem about as hurried, harried and stressful as ancient Israel's Biblical flight from Egypt.

By the way, pet fish have a modest layer of fat, which their wild cousins seldom enjoy. We really don't have to feed them (fry excepted) for several days. If their temperatures aren't high and they have no where to go, bring cold-blooded, they will burn relatively little energy (food).

An example of this was the 2.5-breeding set-up I had brought a pair of Aphyosemion ahli (red) over in. They had a spawning mop, three inches of water and a disconnected sponge filter and fortunately a snug Plexiglas cover. In the sound and fury of scooting everything into this house, they got shoved onto a shelf with sliding doors. And they were forgotten. About a month later, while wondering what was in that cabinet, I opened that thing. The pair indignantly turned my way with a look to suggest, "WELL?"

They were rewarded with a larger planted tank where they comfortably lived out their lives. They and their descendents provided a steady supply of youngsters for a couple of generations until I quit whisking them out of that aquarium.

Before our next move (hopefully some years down the road), out of this house, I may look up some newer and younger aquarists.