Yeah, starting on a hill on any kind of bike is not as easy as starting on the flats. You will eventually get better at it of course and you'll also learn at what slope it is impossible to start from a cold stop on. When you throw in loose gravel, rain, or even wet leaves then it can get pretty hairy. Mainly, I bought my V20 for speed, and where I ride it is about as flat as you can get. I have taken it up towards Mt Fuji area, and I think the total elevation for the ride was 1800 meters. On paper before the ride I have to admit being a little nervous seeing those numbers when I plotted it out on the maps. However, 2 things made the ride enjoyable. I mentally prepared that I wasn't going to be as fast as my road bike on the steeper climbs (which wound up being anything steeper than about 3%), and (2), to just NOT STOP UNDER ANY CIRCUMSTANCES on steep slopes so I do not have to deal with cold starts.
With that said, some complain about wheel slippage on cold starts on FWD bikes including MBB (Moving Bottom Bracket). It does exist. But one way to reduce or even eliminate it other than what I wrote above is ease in to the power when starting from a cold start instead of mashing on the pedals right off the bat with as much as you can muster. On another site this topic came up about MBB wheel slip and I wrote that it is even possible to make a road bike get rear wheel slippage either on gravel or on a cold start in the rain on a slope maybe even with some leaves, but under those circumstances roadies know to ease into the power then. But for some reason they don't want to do the same thing on an MBB. When I got wheel slip on my road bike I didn't throw my bike in the valley and curse the owners of Litespeed. I believe there are other issues at play but you can't teach an old dog new tricks so I mostly stay away from there as they are all about trikes now. Anyway, I digress. Keep up with the low speed maneuvering, starting from cold starts and figure 8s in a parking lot. You'll find that at speed your S40 is going to be very stable.