Thanks for the info guys, looks like 12 is a good starting point. For developing, I have an old Nebro tank with adjustable spiral and one of the settings is for 116 which is the same width as 70mm.
For developers, I have Fomadon LQN, Fomadon LQR, Ornano ST20, Microdol-X, Celer-Stellar and RO9, I'll start with the Microdol-X and go from there.
Yup, I got this on ebay. I've seen the GAF stuff, tempted to grab some, but shipping to England makes it not so cheap.
I missed out on 150ft of Agfa Ortho 25 last week, German seller and he wouldn't accept paypal, and doing an international bank transfer can get expensive.
I'm on the hunt for more 70mm, I mostly shoot BW, but I have several 100ft rolls of Fujichrome duplicating film in the fridge so I have lots of E6 in 70mm.