Join Date: Oct 2010
Location: Victoria, Australia
For the vallisneria if you are just using gravel I would go with some root tabs as they will definitely appreciate it.
Otherwise all of the plants you have listed really require only a basic level of care so you should be able to get away with just dosing Seachem Flourish (the comprehensive fertiliser). Potassium, nitrogen etc. are only really useful if you start seeing deficiencies.
Floating plants however can be a little more nutrient hungry because some of them grow particularly fast. Things such as duckweed, hornwort, frogbit etc. will most likely show deficiencies before any of the other plants.
A good floating plant that would probably be better suited to your tank would be water sprite or water wisteria. They will grow quite happily floating and don't make a mess like hornwort and duckweed can.