Personally I would still get coroplast for at least the bottom. Even though they have solid sides, there's still the holes in the corners, and a hedgie could trip on those. In case hedgie decides burrowing under liners is fun, or pees in the corners, or pees under the liners, etc. then you won't have to worry about mess leaking out of the cage either.
At least a 2x2 is best for a minimum size, but 2x3 is at least as popular, if not more. Lily had a 2x2 for a short time, and was quickly upgraded to a 2x3. Once you get them used to it, I don't think the 2x3 is really considered too big in terms of space & hedgie comfort. Lily wasn't much of an explorer, but she enjoyed the size, I think, and ended up taking advantage of it when I started doing our treat hide'n'seek game.
Heating can be difficult sometimes, but the solid squares might make that easier. You'll want two 10" lamps for a 2x3 cage size to make sure the cage is evenly heated. If you get the 1000-watt Zilla thermostat, it has three outlets, so you only have to buy the one thermostat to control both lamps.
What are you going to do for the top? I wouldn't use the solid ones for the top as well as everything else - even with the corner holes, that doesn't leave much for ventilation. And you do want a top on it since if hedgie is an escape artist, she'll easily be able to escape from a C&C cage with no top. It'll also make it easier to heat the cage with a top (you can just set the lamps directly on a wire top).
~*~*~ Kelsey ~*~*~
RIP my sweet Lily ~ 6/12/08 - 1/20/12