So I ran in to the problem with the +5V input that the TPS requires. The AXE7245 controller has the throttle input 2 connected to battery negative internally, so I can't use the +5V provided by the original car wiring, since it has negative in chassis ground. I received a cheap 12V to 5V converter I bought from ebay, but as I suspected it wasn't isolated. So I put in an order for a 72V to 12V converter, which I could use to power the 5V converter. That way the isolation is not a problem, because I don't have to connect them to the chassis ground at any point. I've also gathered a number of AC to 5-12VDC converters, which I'll test for use with voltages between 48V and 84V DC. If an old Nokia charger will do the trick, maybe I'll just use one.
In other news I've decided to build a better bottom balancing system. Or actually a bottom balancing system, since before I did it by hand. Then I had 25 40Ah cells, so it wasn't too bad. Now I'll have 50 40-60Ah cells or 25 100Ah cells, and I'd like to do it as well as possible, so an automated system is in order.
The parts needed include a programmable voltmeter and a big resistor. I ordered a 0.2 ohm 50W resistor for a couple of euros and a cheap voltmeter with hopefully usable relay control for about 20 €. Both from ebay. Those two combined with a simple automotive 12V relay and a 12V power supply should be quite capable of draining LiFePO4 cells at about 15A or 50W. I'll just set the voltmeter to disengage the relay at 2.5 V and engage at 2.8 V. I should then end up with a pretty much empty cell resting about 2.75 volts.