I currently have 30 clowns (~6 7-8" and the rest between 3-6") in a 150x70x60 tank, including several large females that frequently lay eggs. At that size they are pretty boisterous to the point where it makes feeding other tankmates difficult. Keeping them in a large group of 10+ is when you really start to see their social behaviour, and anyone who says they're alright in smaller groups has obviously never kept a larger group of them. That said I have kept them in various sized groups, including two ~4" together with no problems. Here's a video taken ~6 months ago, I will try to get a more recent one soon; http://www.youtube.com/watch?v=vYxbPrsWvL4.
Those 20 small clowns you have on hold will be absolutely fine in a 4x2x2 tank for a few years. In fact you could probably double that number for at least 12-18 months before you would want to upgrade the tank or start thinning them out. They will actually grow quite quickly from a small size up to around 5" provided they haven't spent a long time in a tiny tank at the LFS and been stunted. Good food and clean water are the keys to success, strong filtration with plenty of current is essential. Long-term they will need something longer than a 4' tank (6' minimum) to give them room to swim and keep them growing, but you've got a couple of years to get that sorted out. I think the biggest problem with the senegals as tankmates (assuming they're too small to eat the loaches) will be getting enough food to the sens once the loaches are larger. Within the next 12 months I plan on having a specific loach tank, which I will stock solely with the clowns and a school of fast and tough mid-level fish (appollo sharks would be nice, maybe rainbows?).
I'm not sure if Charlie or the online stocking tool have ever kept clowns, so believe what you will Morcs, I'm just relay some personal experience..