I also started developing color films. And it can be done, and quite easily. I have the Jobo 1520 tank for roll film and also have developed color C-41 sheets in HP CombiPlan tanks. Worked reasonably well for me with the water bath as you mention it.
As to the amount of chemistry, for the Jobo tank and rolls, it's easy - just follow the instructions, 500ml of chemistry, and you can run up to 6 rolls in it. The HP tank takes 1l of chemistry (for 9x12cm sheets. For 4x5 it should be 1250ml) and I convert it according to the surface area. I calculate, that a roll of 120 film is approximately 480square centimeters. For sheet films, one 9x12cm is roughly 108square centimeters. So I calculate that 1roll is equivalent to 4 sheets.
And you can develop 6 rolls in a 0.5 l of chemistry, and that should be the same as 24sheets. But for my HP tank, I need 1l of chemistry, and that is 48sheets.
My reasoning and calculation could be wrong, but I have developed C-41 films this way. And all was OK.
Just 2 days ago I did also my first run on E-6 rolls, first six of them. In Tetenal kit. Also came out OK.
As far as keeping the temperature, I would recommend buying those plastic temperature keeping box for food. I fill them with water at around 45-50°C, put the chemistry in bottles, close the lid, and let it temperate for around an hour (with checking the temperature not to drop bellow 40°C). The box keeps the temperature much better, and also, you need less hot water.
I start with the developer at 39°C, and if the during the development the temperature drops to 37°C, everything is OK, the average is required 38°C.
To see the results, check my gallery, those two color pictures are both developed at home in a C-41 chemistry...