On the brakes, running a single lever with two callipers won't work, as the piston movement will be halved.
There are 3 manufacturers of special one lever/two brake systems that I know of:
-Magura Big Twin:
http://www.magura.com/en/controls/produ ... aulic.html
-Tektro Auriga Twin:
http://www.tektro.com/_english/01_produ ... &fid=1
-Hygia Multi:
http://www.hygia.com.tw/prod-brake01-4.html
They are all designed to operate equally on both brakes (Double front discs or paired trike wheels) so you'd need to put a
brake proportioning valve at the hose splitter to distribute the pressure...maybe 40/60% favouring the front, otherwise the rear wheel will lock.
On the gears:
-use a multi speed twist grip gear...Shimano Alfine, Sturmey,
Nuvinci etc, or if you're feeling flush a
Pinion drive equipped bike.
-Or the Alfine Di2, which just has push buttons
-Or the new Shimano electronic stuff which can be programmed to be fully sequential over two mechs with just an up and down button.
-Or really oldschool: the
EGS Synchroshift... two mechs, two cables, one twist shifter.
Legally, as it would be an adaptation for disability use, a new bike with any of this work done could be exempt from VAT, too. Also any BS or EN retail product rules are bypassed as it's a custom product, so you don't have to run 2 separate brake systems like the rest of us.
Lost of set-ups here:
http://www.mtb-amputee.com/bikemodifica ... _Amputees.
All the best,