How long should i give the plants before I become worried about not seeing any growth?
Maybe a month or so? With this low light level, growth won't be quick, though you should get some.
What should i add first? RCS or the Neon Tetras?
I'd add the shrimp first - and I wouldn't add the Neons till the shrimp have at least a decent amount of plant cover grown in so they can hide from the tetras.