You can't really compare an 810 to a 35mm, 10x enlargement. At 20x24, you will be making a 2.5x enlargement with a neg that has over 50x the area. You need alot more light than 300W. A 1212 coldlight is about 200W and it is many times more efficient than a 300W incandescent. I agree with Donald, you will need 1000W of incandescent to use this enlarger with 810. I don't know about all the other light sources or enlargers. I have a Beseler 45M modified to take the 810 adapter. It works fine, prints fast, and fits in a small darkroom. Because of the diffused light, negative defects and 6 surfaces of dust and dirt and Newton rings don't show up. A point source or condenser will accent dust and defects.
Maybe you should start by contact printing. Nothing better and 810 is a nice size.