Multi day event training

Two-Stroke Tart

Hello!  I appear to have agreed to doing the new Half Marathon Des Sables in September next year, but I've never done back to back races before and was hoping you lot may be able to give me some help!  I've done a couple of marathons, but that was a few years ago and my running has been a bit sporadic since due to some injuries.  I've been doing a load of rehab stuff since September last year with a sports therapist and hopefully that will go a long way to stopping future injuries.  So, I'm back at the beginning again and with 16 months before the Half MDS, and about 14 months before Race To The Tower which I was thinking of doing in June next year as a kind of practice.  I'm planning on run/walking the events rather than running, so planning on doing my training like that. 

What I have no idea about is should I do all my training as back to back runs?  The Half MDS is four runs over four days, with one at night, but as yet they don't appear to have released the distances of each stage, just that the total distance will be approximately 75 miles.  Once I have a better idea of distances, should I match my training sessions to be proportionate to those distances?  I have a fair amount of work to do in terms of increasing my mileage to get to the distance, given I'm only just at the 3 miles a session stage, but I figure I have long enough to do it without increasing it too quickly and doing myself a damage. 

I'm what I like to call tenacious, although my husband likes to call it pig-headed stubbornness, so I'm sure I can do this, but as I don't really know where to start I'd be really grateful for any help you could give me!