newts might be ok with such a small land space, they typically like more water then salamanders. as far as a heater it would be quite the opposite, if anything they would need a fan and a chiller, depending of course on the room conditions. they do like it quite cold most of the time though.
as far as the crabs, dont mix them with the newts of course, but you might also want to look into vampire/carnival crabs, though i believe they like more terrestrial conditions.
riccia might do well and should grow out of the water. creeping jenny is another. i forget the name and dont feel like looking it up, but another plant that should do well is that vine you see...well... everywhere. next time you see your doctor or dentist check it out...ugh, ok im looking it up right now...epipremnum aureum. there are tons of "bog" plants out there like purple waffle, green sandy, peace lillys, but i dont have much experience with them so cant recommend them.