If I had 900ml of liquid methylamine I'd use it for something else, I can guarantee you that much. :P
Yes using methylamine as the solvent would be a little extravagant. But who said that you have to? Bee's who have been running Birch type reactions are using great substitutes. NH3 will work fine, basically as long as the solvent can dissolve and doesn't react with the Li metal and the salt, your in business. There are plenty of potential solvents that Chem Guy has found. https://www.thevespiary.org/rhodium/Rhodium/chemistry/birch.notes.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/birch.notes.html)
Of course some will react with the electrodes, but this a good thing, it's better to be reacting with a polar aprotic solvent than chewing your molecules to bits. In fact in one of the refs above it goes in to quite a bit of detail about the destruction of their MeNH2. I would stick to the amines as the preferred solvents such as ethylamine and EDA
Remember your dealing with an indirect electroreduction process, not a direct reduction. Meaning the thing your worrying about is making Li metal which does the rest, the electro set-up has nothing to do but recycle the Li salt. It plays no other part but that.
Ok, so 85V * 2A = 170W heat generated. Ouch. Good luck keeping that reaction at -7°C without losing all the MeNH2.
Yes that is pretty shitty. In fact I really have no idea why they used that particular set-up. I've seen industrial electrodes which were huge and they were closer together than these (they had then 150 mm apart, this was also the reason for using so much MeNH2). So to solve that problem just move them to about 1 cm apart, I suggest using platinised screens these are easy to obtain and won't interfere with stirring so much. You will probably have around 3 to 4 volts across the electrodes at that proximity. If the resistance is still to high add more LiCl to lower it, or maybe add a second supporting electrolyte.
I also wouldn't get to hung up on keeping the reaction temp at -7º C. I believe this had more to do with keep the methylamine in the flask than a critical temp. Since it is an electro reaction you can control the rate and time.
The one big mystery is the selectivity, would the reaction just reduce your imine or would it reduce everything? You can limit the time with the imine hopefully being target No 1 but if it is not, it isn't going to work with MDP2P/P2P's