I meant since I use 4x5, my choices would start with the 4x5's, rather than the 23C's, but my choices may not be best for you.
By complete I mean that it comes with negative carriers, mixing boxes, power supply, etc. For the Ilford and the color enlargers, the power supply and control box (in the case of the Ilford) are essential, they don't function without them.
The 23C may not be able to get to 16x20, but getting to that size for the others should be no problem.
Your 7 foot ceiling might be a problem for the 4x5's, depending on how high you build your work surface. The head will extend several inches above the column as you move it up for larger prints. The columns are 3 + feet high.
For variable contrast paper, built-in filtration is easier than swapping filters in and out, so many folks use color enlargers to use combinations of yellow and magenta filtration for the different contrast grades. The Multigrade head makes this easier yet, since the filtration is specifically designed for VC papers. The difference is that with the MG head you just dial in the contrast grade you want. For color heads you must refer to the information sheet with the paper, and adapt the filter values to your particular enlarger.
It's harder to describe than to do it though.
The only difference between the chromega, and the ilford is the head containing the filters, and maybe the mixing boxes. The column, focus mechanism, etc are exactly the same.
$20 for a 50 mm 2.8 El Nikor is a good price.