First off, the tetras and cories need groups of 6, but Im pretty sure that would be too much.
I also wouldnt have both rams, and would stick to one kind. German blue rams are very sensitive to organic wastes (ammonia, nitrite, nitrate) so I wouldnt recommend them to a beginner.
What kind of cories? Several are small enough to be kept in your aquarium. Im not sure the species but someone else can say.
The assassin snails need other snails to eat. Instead I would get some nerites, as they are excellent for eating algae and cant overrun your tank as the eggs only hatch in brackish water.
I wouldnt do a pleco with rams, as plecos are quite messy and rams are sensitive, they will create quite alot of nitrates. They also need a softer wood to rasp, and if you dont have that then dont get them.
Sorry to be so negative, and, Im not sure if Im right, just been googling. Im also not sure for stocking suggestions