I uppgraded and improved my electric blast furnace a bit with the border sharing on the multiblocks
I went from 3 to 6 without that much of an investment. It was a nice exercise in learning how to make combined multiblock structures
http://prntscr.com/arull2
They can actually share all the different input/outputs with eachother, however you cannot do it with all slots. For instance the front side has 7 slots available so my solution was to make it share 3 input busses and 2 output busses and 2 single output busses. Im gonna automate the input into the blast furnaces from a shared chest that sends out with round robin settings. Since some of them will be dedicated to steel and some to titanium i will also do a blacklist filter on the input slots so titanium/wrought iron gets sent to the correct input bus. i will make a similar system for the output where all hot ingots get sent into the freezer with a higher priority white list and everything else get sent into a buffer chest
The backside is a bit more complicated. Like the other side only one input that can be shared in sets of two across all of them. For the ones shared by 2 blast furnaces each i choose power since one HV input hatch can recieve 2 amps so it makes sense to power 2 blast furnace with every input hatch. Every blast furnace also has its own maintainance hatch straight in the middle and input hatches has the same configuration as the output busses with 2 shared and 2 single.
http://prntscr.com/aruq3g
ive set the side blast furnaces to make steel with oxygen and the 4 middle ones to accept the titanium liquid when i make titanium ingots.
This was my prefered setup but you can actually share the inputs however you please and i could just as well make them share 3 maintanance hatches and use 6 HV input hatches in the middle instead so it is rather flexible
You could also fit one additional blast furnace within a chunk border but that is where the limit is so its probably best to avoid making more than 7 in a row.