Through Jesus, anything is possible. Can you win an aquascaping contest with a low-tech tank though? I highly doubt it.
If the goal is just to win a contest without CO2, your best bet is to enter a biotope contest. Paludarium contests are also more forgiving for lower-tech plants due to the limitations on lighting. And of course you don't need CO2 for a wabi kusa.
Medium amount of light, no CO2, and ferts. In other words, is it possible to have a good hardscape but instead of hard plants, you use easy plants. Or would the large amounts of plants require higher lighting and CO2? Thanks.
It's a very ambiguous question, so it's going to be tough to answer. What contest are you talking about here?
You can certainly use easy plants with good hardscape. I don't think I've ever seen a tank with "hard" plants in top 27 of the IAPLC, people aren't growing rotala ramosior, hygrophila "chai," syngonanthus species etc. The challenge is getting dense, healthy growth from the top to the bottom of a diorama style aquascape. You need a lot of light for that, and it's most likely going to cause algae problems in a low-tech (or what you would call medium tech) tank.
What is Jesus phone #; i need to request a miracle.
While not complete most of the 'contest' tanks you see have a lot of red plants and those usually require richer substrate and co2. Some sort of colourful plants will grow in a low tech tank but they are limited in my experience and lack the 'wow' factor we see in some of these 'contest' tank. But of course if you enter in a contest for non-co2 tank the story is different.
I think the most important thing to remember is to keep it fun and enjoyable. And also keep in mind that almost no one winning a scape contest got to that point without a lot of trial and error - the fun stuff. The only way to get there is to try.
Hope you'll consider starting a tank journal so we all can follow along.