Make sure if you use Steel that it is at least 3" tube steel. It will really spread the weight of the tank on the floor. Personally I would use 4" for a tank that size. I'm using 2" 1/4' THICK, but my tank is only about 550 gallons. YEs technically you could use smaller, but remember going from 2" to 3" would spread the wieght on the floor by 50%. That would be a huge help in the weight distribution.
You would need someone who knows weight calculations to help you with the final tube size and thickness.
The rhino liner is much better that the powder coating in my openion, it does not get knocked off easy and unstead of being paint thickness like with coating. It is about 1/4" thick on mine.