Try checking out the MAX7221 chip. It's pretty expensive ($10) but you don't need to wire up resistors for the LEDs (save one for setting current) and you can just send it a string like "09221" over SPI (three pins) and it'll display them (ie a 7segment decoder). It can handle up to 8 digits (and you can string them up without using any extra arduino pins). It'll also do a LED Matrix if you like those.The only other reasonable option from a string of breadboards is to have a custom PCB. And if you go with the breadboard route, the wiring will get pretty intense. Then again, custom PCBs are scary and somewhat expensive.Also, you really don't need to worry about update speed; I doubt anything you'll have will be slower than the PC Serial connection, and you can only really perceive updates more than about 50ms apart (I believe that's 80000 clock cycles).
You want 30 7-segment displays? Yeah, 4 MAX7221's will do 32 digits nicely. Or 5 for 40.SPI commands to all of them, can control data update to each digit.Lot of commonality in the wiring, be straightforward to do, either as wirewrap, or spread across a couple of 80x100mm PCBs.
On the other hand, 6.5" / 12 = 0.54" wide.0.8" tall digits are 0.787" wide.a 0.56" tall digit, 4 digit display is 1.98" wide, so 3 displays (12 digits) would fit in 6".http://www.kingbrightusa.com/category.asp?catalog%5Fname=LED&category%5Fname=KC4%2DDigit+0%2E56in&Page=1
Did you price them ordering direct from kingbright?I've purchased from them directly.
Yes.I find common anode easier to deal with.Anodes go to +5, cathodes go to shift registers that pull low.