Here's a belated welcome to The Planted Tank!
Here's what I would do if I were in your situation, given when you've told us here and me via PM. It's not a fast process, but it will build a solid foundation for long-term success.
1. Get the tank set up dry and clean the hell out it and all the hardware with white distilled vinegar. Don't do this to the filter until you've taken all the media out.
Dump the rest of the vinegar in there, fill it up, and let it run for a few days. If you're in an area of hard water and there are deposits on the glass, get a few gallons of vinegar if affordable in your area to dissolve some of the deposits and loosen the rest of them up for cleaning.
2. Forget aeration. Erase it completely from your mind. This is one of the counter-intuitive things I mentioned. We may come back to this as a possibility later, but for now consider it a non-option.
3. If possible, contact the person who's keeping the tank now and request they continue running it until you're ready to pick it up. Siphon out and save all of the mulm and detritus from the aquarium and filter. That stuff's worth its weight in gold and will go a long way toward establishing your biological community.
4. You mentioned using soil in the 10 gallon. You're in luck, that's what I did my graduate thesis in. I'll be happy to tell you aaaaaaaalllll about growing aquatic plants in soil if you want. For now, let's consider the pros and cons about using soil in this tank, and I HIGHLY recommend using soil in this system given what I understand of the hardware.
a) From your description is sounds like this system is what we plant hobbyists consider "low tech", meaning it will have little to no plant-specific hardware to support growth. There's nothing at all wrong with this. It's absolutely possible to have an attractive and enjoyable planted tank with little in the way of supporting hardware. Planted tanks, especially low tech tanks, are ecosystems, and ecosystems take time to recover from a disturbance. Plan ahead, have patience, and if you must make changes, make them slowly and infrequently. Oftentimes just letting things be will fix things.
b) Tanks with a soil-based substrate (hereafter, soil tanks) need time to mature. There are going to be all sorts of biological and chemical things going on in the soil once it's submerged. Letting it sit for a couple months wouldn't be a bad thing. The initial nutrient release is a perfect way to cycle the tank without fish. Yes, the soil is going to go anaerobic; it's inevitable and is not a bad thing from a chemical and biological perspective. It's a natural part of the ecosystem you're building and is part of the reason you want to let it mature.
c) Cons of soil- loaches can disturb it and your Red Tail Shark is a loach. How can you mitigate this potential issue? A thick sand/gravel cap over the soil.
d) How would I prepare the soil and cap to best keep plants and fish together? 1- Get a couple bags of cheap organic potting soil and sift out the fines with a kitchen colander; mix it 75/25 soil/gravel then pour the mulm/detritus over it and mix it well. Sifting is an important step as the large bits will cause issues with the soil maturation and are a potential source of issues over time. I, and a number of friends, have found that mixing gravel in with the soil helps reduce compaction that would otherwise take up valuable resources from the plants. (This is a pretty technical topic for a later date). Depending on the color and amount of the gravel that's coming with the tank I may or may not use it. (I'm not a fan of gravel that doesn't look natural). If you're cool with using it, go for it; it's YOUR TANK so do what it takes for YOU to enjoy looking at it day in and day out. Caveat- you'll need a cap of at least 5 centimeters of 2-4mm gravel to make sure the soil stays in place.
This is non-negotiable. I'll be happy to explain why later, but for now keep this as a rule to follow. Anything smaller than 2mm will cause issues with diffusion into and out of the substrate that will help to keep the soil ecosystem healthy and nutritious over the long term.
e) Cheap sand option- If you've got access to a local stream and are feeling burly and ambitious, take the colander and a couple buckets down, sift out the sand there and use it for a nice natural looking substrate. The sifting automatically gives you the proper size material to both mix with the soil and use as a cap. Easy, peasy, breezy, and beautiful. If you feel the stream is clean enough, you may consider using it raw to include the microbes from the stream. If not, rinse it well.
That's enough for now. I'll write more later.