Motobecanes are most excellent bikes, easy to wrench, aside from the cam/clutch puller (mandatory tool to get) you can easily fabricate any other specialty function tools in a garage without access to a machine shop.
Master switch from hell needs to immediately be replaced if it has not already failed, this will also require hard wiring the bike with the added benefit of chasing out all the other electrical gremlins designed into the bike by evil French electrical engineers (an evil deed by the French in retaliation of the US DOT forcing them to have the ignition ground through the tail light and installing a sealed beam headlight).
You will want to at least install an external condenser as the original design with an unvented magneto just cooks the poor heat sensitive unit in the heat byproduct of electrical generation. You would also need to replace the bonding strap that goes from the upper engine mount to the external coil with one from a intake to that coil (which happens to be the best location for that external condenser).
Check the engine mounts - the rubber gets soft and they distort to the point where full variation is not possible. Replacement is a 15 minute job if you have trouble... shorter if you set yourself up properly and not try to take short cuts.
Swapping out the Gurtner carb for a SHA14:12 is a good idea, unless you have the patience of the Dalai Lama and want to clean that dang weepy carb to surgical standards. Best idea is a cable choke carb.
Check the head badge of the one you plan on buying to ensure it is at least rated at 30mph as Mobys come in 3 flavours 20 - 25 - 30 miles per hour ratings in either variated or dimoby single speed. If you get the rarer dimoby 30mph bike you only have to put on a stock variator and change the Jhook and you can laugh at the folkes who snickered behind your back for getting the cheaper version because you will be instantly faster than their stock 50v.
Like any bike, some folks love them, some like them others hate them... like any other brand they have their particular issues and characteristics which some folks cope with, some manage well and others just get angry.
They have a reputation of being temperamental and moody little Frenchis bitches who will give you much love when they are in the mood and grind you the wrong way at other times. All so very true but they are drop dead sexy and so much pleasure when they are well loved.
^ in my humbly unbiased opinion...