No, there is no minimum; they will all pull a cart. BUT what do you intend to load the cart with?
If you have level ground and plan to use a small cart to pull mulch, or other relatively light stuff such as a dethatcher, spike aerator (and perhaps a very infrequent heavier load) then the 1042 should suit your needs fine.
If you plan to pull heavier objects on a somewhat routine basis (more than a couple times per year) and use things like a plug aerator, have uneven terrain, etc. then consider the 2542.
In any case, both are good machines for their intended purposes. If you have the extra $, go with the 2542 (or consider the 2544 for the deeper deck (yeah it is 2" wider, but it is also a LOT deeper). It is quite a bit more tractor.