it still stop after 2 minutes, so not a big problem. afaik there are many "lift detector" malfunctions then train stops immediately after start, so lego decided remove it. sometimes a little force needed then you have a big train with about 10 wagons and 1st wagon must be with new hook. yes, I know. this was more "proof of concept" than really needed item. if you don't have rails — yes. but if you have — child put train on rails immediately after box unpacking. 1. yes. points, crossovers and possible — bridge are problem for car bases.2. there are many push-train sets with train bases, last one — [6144]. so I don't see any reason to use car base in push train set except price of course.
3. btw there is another un-understandable story for me with push-trains. all push-train in last ~10 years have originally reversed bases — movable hook is at backside. this is not a big problem for sets with train bases, you can put base in correct orientation and everything works, but for [10558] this trick doesn't work. but old sets like [2452] have correct direction.
yes, duplo has only one scale for humans. but there are at least three types with minor differences:1. before 2004 year released ones.
2. after 2004 year type 1. possible produced in hungary.
3. after 2004 year type 2. possible produced in china.
old ones looks like don't have serious bugs. new womens have a big hairs, so they can't look forward in all duplo cars. also type 2 humans better fits into animals or old style motorcycle passenger place.