when you start to get a bloom of some kind in your tank it is past time to add snails (i like hermits also but some have had bad luck) to get rid of it. IMHO of course

4-6 weeks is probably good. as long as the nitrites and ammonia are 0 and the water smells fresh. i would put a bag of carbon in a
high flow area to absorb toxins for the first 6 months. customaquatic.com has a house brand that is cheap and works well. not on the web site just call them. in fact after 2 years, i started using carbon again. with all of the softies in my tanks and the resulting chemical warfare i find that it decreases my water change requirements by a factor of 3 and keeps the water nice and clear and smelling fresh.
bill