Hi Noah,
Starting with the simple parts of the question, the cupro-nickel pipe you mention is what I use on all my brake lines, and is fine for the Elan (soft enough to work with, corrosion resistant, and copes with the pressures. The Elan comes from the factory with steel (coated with something or other to protect them) brake lines - but once they start to rust, they cannot be 'shortened' at home and re-flared - unless you happen to have industrial tools at home! Fortunately, there are quite a few junctions/unions along the way. so no huge lengths are required.
I have never worked on a FED car, so my comments are based on a UK car structure (but don't expect it to be very different).
On a UK car, the MC has 4 outlets (only 3 on a FED car) which go to each corner........ and then they go through a junction box under the wiper motor, and then to each corner...... depending on which line you are changing it may be one piece from the MC to the wheelarch, or it may be in 2 pieces - and how many you replace are up to you. I have changed all of mine as the OE ones were past their best, and it's easier to do them all in one hit.
The fittings are mainly an M10x1.0 (standard Metric) thread - which use an 11mm spanner on a male fitting, and a 13mm on a female (7/16" & 1/2" will work) - with the exception of 2 ports in the MC which have M12 male fittings. Although it may be possible to re-use the old fittings, they are cheap enough to buy new ones....... many 'kits' on ebay/Amazon will have the flaring tool, pipe and fittings included..... something like this for £22 -
https://www.ebay.co.uk/itm/388867501092It is not necessary to get the bending tool (although it may make it look a little neater) - the pipe is bendable with finger pressure, and I use a variety of sockets to form the right radius by simple wrapping the pipe round them.
There are 2 types of flare (well, more than that - but 2 types used on the Elan) - a male and a female - each are made using a similar process, which is explained fully in the paperwork with the flaring tool (the exact measurements of 'extra' pipe required and how to measure it varies with the particular tool, but all are very similar). It is obvious when you see them which is which.
My advice for anyone who has never done it before is to use a short length of pipe and practice the flares a few times before making the pipe you need - it is easy to tighten up the tool too much and wreck the joint by 'thinning' the metal - less is definitely more!
It may be really obvious, but make sure that you actually put the fittings on the new pipe before you do the second flare........ if I had a quid for every time I've had to cut the end off and start again I'd have a nice pot of cash by now!!!!
There are many different types of flaring tool available, but there is no need for you to buy an expensive one - a garage making them daily may have a bench-mounted unit, but the small hand-held ones I linked to are easier to use in a tight space under the car. I have both types, and can't remember the last time I bothered to open the box for the "decent" one - even when changing a whole cars worth of pipes.