Wait till ammonia and nitrite hold at 0 for a few days then add a small CUC.
For algae I recommend turbo snails and astraea snails. For fresh uneaten food I recommend nassarius snails and for detritus and older food the nassarius don't like I recommend ceriths. Hermits are good for uneaten food too, but some people have issues with them. A personal favourite of mine are the sea urchins, but they need a large and well established tank.
Start out with a small CUC and add more if you need to. For example, in my 120 I plan to have 2 turbos, 10 nassarius, 2 hermits and about 10 ceriths.
A lot of people are adding hundreds of snails to their tanks and wondering why they last a few weeks then die. They don't realise there was only enough food for a few weeks then they starved to death. If you start slow you can adjust the numbers of each species to find a balance between how fast the food supply is being eaten and how fast it can grow.
Best case scenario would be to add your carnivorous CUC during week one of the tank being able to support life. That way you can feed them and develop a small amount of algae so when you add your herbivores during week 2 or 3 there's already a supply of food for them. But this isn't always a realistic plan.
The brown stuff is probably the diatom bloom. This usually happens at around 3-6 months into a new tank but can happen earlier. It should die off on it's own.
The green hair algae will need to be cleaned up by a mixture of the CUC, water changes and manual removal.
Good luck!
