I hope you got a thermostat to regulate that heat mat. If not, please do so. Some of those heat pads (depending on brand and size) can hit 140 degrees. I have 3 Heat pads all various sizes, and they all range from 122 to 137 degrees. That kind of heat can kill a snake. That's why we all use thermostats to keep the desired temps.
I used to use Newspaper 45 years ago as Aspen was not available and everyone back then used newspaper. Some folks still do. Some folks use paper towels. Some folks use Aspen, Eco Earth, and similar products. As long as it's nothing toxic, I don't think it really matters. Personally today, I use "Reptile Carpet." I bought 2 sheets of it 5 years ago and I'm still using the same 2 pieces. No more Aspen all over the house. I don't have to buy it in bulk. When 1 piece is dirty I put in the clean one. I always have 1 ready. But that's just my preference. A lot of people think Corn Snakes need to burrow. That's not true, They will hide, But I'm yet to find a wild corn snakes burrowed in a field of shredded aspen.
As long as you provide plenty of hiding spots (multiples) the substrate really doesn't matter. Corn snakes like small tight places to hide in. You can replace them with larger hides as they grow. But even the larger snakes like a small tight hide. Try to have at least 1 hide over the heat pad, 1 hide on the cool side, and perhaps 1 or 2 more in between.
Lots of those fake plants and vines make the tank look pleasing, the snake will like ti too. Corn snakes like a lot of clutter. If you can look in the cage and easily see the snake, then the snake will not be comfortable. Especially small babies. They are vulnerable and prefer to hide. Until the snake gets to know you and trust you, it will regard you as just another big animal trying to eat it. So don't be surprised if it stays hidden, runs from you or even bites.