I have currently 310 places at stables (used some Expand Stable Scrolls and Kamis),. Would buidilng Stable lvl5 now increase the pet limit , or would it reamin the same? Are additional expansions summing up with the stables limit or the order matters and after using expansions there's no point in building higher level stables?

All types of expansion are independent from each other, so building Stable level 5 will increase your pet limit.

thank You very much for the answer!