"Would an Uno meet those needs for I/O"
Make up a list of the I/O needed for each device. Count the number of pins.
Need <20? Uno. Consider Serial interface display to save on pins also. www.newhavendisplay.com
Need 21-32, dual hardware serial ports, and still low cost? 1284P based design. (Also has 16K SRAM, twice that of a Mega)
33+ IO, Megahttp://www.crossroadsfencing.com/BobuinoRev17/
bare board $6, processor ~$8 at mouser.com, scrounge your parts bin for the rest, or around $15-20 total at mouser.
(I may do these up as a kit too)